Method and apparatus for body fluid sampling and analyte sensing

ABSTRACT

A method of controlling a penetrating member is provided. The method comprises providing a lancing device comprising a penetrating member driver having a position sensor and a processor that can determine the relative position and velocity of the penetrating member based on measuring relative position of the penetrating member with respect to time; providing a predetermined velocity control trajectory based on a model of the driver and a model of tissue to be contacted. In some embodiments, a feedforward control to maintain penetrating member velocity along said trajectory.

This application is a divisional of U.S. Ser. No. 10/559,223, filed May5, 2006 now U.S. Pat. No. 7,850,621, which is a §3.71 filing ofPCT/US2004/018132 filed Jun. 7, 2004, which claims the benefit of U.S.Ser. Nos. 60/476,584 filed Jun. 6, 2003, 60/478,040 filed Jun. 11, 2003,60/478,704 filed Jun. 13, 2003, 60/478,657 filed Jun. 13, 2003,60/478,682 filed Jun. 13, 2003, and 60/507,689 filed Sep. 30, 2003, allof which applications are fully incorporated herein by reference.

BACKGROUND OF THE INVENTION

Lancing devices are known in the medical health-care products industryfor piercing the skin to produce blood for analysis. Typically, a dropof blood for this type of analysis is obtained by making a smallincision in the fingertip, creating a small wound, which generates asmall blood droplet on the surface of the skin.

Early methods of lancing included piercing or slicing the skin with aneedle or razor. Current methods utilize lancing devices that contain amultitude of spring, cam and mass actuators to drive the lancet. Theseinclude cantilever springs, diaphragms, coil springs, as well as gravityplumbs used to drive the lancet. The device may be held against the skinand mechanically triggered to ballistically launch the lancet.Unfortunately, the pain associated with each lancing event using knowntechnology discourages patients from testing. In addition to vibratorystimulation of the skin as the driver impacts the end of a launcherstop, known spring based devices have the possibility of firing lancetsthat harmonically oscillate against the patient tissue, causing multiplestrikes due to recoil. This recoil and multiple strikes of the lancet isone major impediment to patient compliance with a structured glucosemonitoring regime.

Another impediment to patient compliance is the lack of spontaneousblood flow generated by known lancing technology. In addition to thepain as discussed above, a patient may need more than one lancing eventto obtain a blood sample since spontaneous blood generation isunreliable using known lancing technology. Thus the pain is multipliedby the number of attempts required by a patient to successfully generatespontaneous blood flow. Different skin thickness may yield differentresults in terms of pain perception, blood yield and success rate ofobtaining blood between different users of the lancing device. Knowndevices poorly account for these skin thickness variations.

Variations in skin thickness including the stratum corneum and hydrationof the epidermis can yield different results between different users.Spontaneous blood droplet generation is dependent on reaching the bloodcapillaries and venuoles, which yield the blood sample. It is thereforean issue of correct depth of penetration of the cutting device. Due tovariations in skin thickness and hydration, some types of skin willdeform more before cutting starts, and hence the actual depth ofpenetration will be less, resulting in less capillaries and venuoles cutand less spontaneous blood generation.

Known lancing devices fail to provide accurate sensing of lancetposition. Thus they do not know exactly how far the penetrating memberhas cut into the tissue. This lack of position sensing is one reason formore painful lancing associated with known fluid sampling devices.

Additionally, known lancing devices fail to have sufficiently accuratecontrol of lancet position and velocity to achieve a spontaneous bloodgeneration in a relatively pain free manner.

SUMMARY OF THE INVENTION

The present invention provides solutions for at least some of thedrawbacks discussed above. The technical field relates to the lancing ofthe finger to obtain a body fluid or blood sample for the analysis ofthat sample. Because the penetration distance is a strong predictor ofthe success of the lancing event for spontaneous blood generation, theability of the device to accurately control this distance is ofinterest. Specifically, some embodiments of the present inventionprovide an improved body fluid sampling device. For some embodiments ofpenetrating member drivers, the invention provides improved methods forcontrolling the velocity and cutting efficient of a penetrating member.At least some of these and other objectives described herein will be metby embodiments of the present invention.

In one aspect, the present invention provides improved lancing devicesoperating with adaptive control algorithms. Because of the very highspeeds that embodiments of the present invention may move theirpenetrating members, feedback control may not be sufficient, due to theshort amount of time available. In one embodiment, the present inventionprovides desired parameters, based on the models of the penetratingmember, the penetrating member driver, and the targeted tissue. Based onthis model, the system may have predictive information stored in lookuptables on how to drive the penetrating member driver and when to applybraking force so that the device performs as desired to arrive at adesired depth and to provide a desired level of cutting efficiencyand/or performance.

In one embodiment, a method of controlling a penetrating member isprovided. The method comprises providing a lancing device having apenetrating member driver with a position sensor and a processor thatcan determine the relative position and velocity of the penetratingmember based on measuring relative position of the penetrating memberwith respect to time; providing a look up table having desired velocitytrajectory based on empirical data; and using control to adjust lancetvelocity to maintain penetrating member velocity along said trajectory.

In another embodiment, the present invention relates to the way that anelectronically driven lancing device controls the trajectory of theinbound lancet up to the point of maximum extension or penetration intoa target tissue. This is the point of maximum penetration of the lancetinto the skin. This embodiment of the present invention comprises acontrol algorithm, that when combined with the necessary hardware toexecute the control instructions, increases the depth accuracy of thepenetrating member. The present invention also provides improved cuttingefficiency by providing lancet behavior that is optimized for cuttingtissue.

In one aspect, the present invention involves learning through testingwhat the ideal setup parameters are and then using more complicatedfeedback systems to get results similar to a feed-forward system.

In other aspects, the present invention may involve manual braking,braking with zero residual energy, braking only, preservingacceleration, and appropriate force for smart braking.

The system may further comprise means for coupling the force generatorwith one of the penetrating members.

The system may further comprise a penetrating member sensor positionedto monitor a penetrating member coupled to the force generator, thepenetrating member sensor configured to provide information relative toa depth of penetration of a penetrating member through a skin surface.

The depth of penetration may be about 100 to 2500 microns.

The depth of penetration may be about 500 to 750 microns.

The depth of penetration may be, in this nonlimiting example, no morethan about 1000 microns beyond a stratum corneum thickness of a skinsurface.

The depth of penetration may be no more than about 500 microns beyond astratum corneum thickness of a skin surface.

The depth of penetration may be no more than about 300 microns beyond astratum corneum thickness of a skin surface.

The depth of penetration may be less than a sum of a stratum corneumthickness of a skin surface and 400 microns.

The penetrating member sensor may be further configured to controlvelocity of a penetrating member.

The active penetrating member may move along a substantially linear pathinto the tissue.

The active penetrating member may move along an at least partiallycurved path into the tissue.

The driver may be a voice coil drive force generator.

The driver may be a rotary voice coil drive force generator.

The penetrating member sensor may be coupled to a processor with controlinstructions for the penetrating member driver.

The processor may include a memory for storage and retrieval of a set ofpenetrating member profiles utilized with the penetrating member driver.

The processor may be utilized to monitor position and speed of apenetrating member as the penetrating member moves in a first direction.

The processor may be utilized to adjust an application of force to apenetrating member to achieve a desired speed of the penetrating member.

The processor may be utilized to adjust an application of force to apenetrating member when the penetrating member contacts a target tissueso that the penetrating member penetrates the target tissue within adesired range of speed.

The processor may be utilized to monitor position and speed of apenetrating member as the penetrating member moves in the firstdirection toward a target tissue, wherein the application of a launchingforce to the penetrating member is controlled based on position andspeed of the penetrating member.

The processor may be utilized to control a withdraw force to thepenetrating member so that the penetrating member moves in a seconddirection away from the target tissue.

In the first direction, the penetrating member may move toward thetarget tissue at a speed that is different than a speed at which thepenetrating member moves away from the target tissue.

In the first direction the penetrating member may move toward the targettissue at a speed that is greater than a speed at which the penetratingmember moves away from the target tissue.

The speed of a penetrating member in the first direction may be therange of about 2.0 to 10.0 m/sec.

The average velocity of the penetrating member during a tissuepenetration stroke in the first direction may be about 100 to about 1000times greater than the average velocity of the penetrating member duringa withdrawal stroke in a second direction.

A further understanding of the nature and advantages of the inventionwill become apparent by reference to the remaining portions of thespecification and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an embodiment of a controllable force driver in theform of a cylindrical electric penetrating member driver using a coiledsolenoid-type configuration.

FIG. 2A illustrates a displacement over time profile of a penetratingmember driven by a harmonic spring/mass system.

FIG. 2B illustrates the velocity over time profile of a penetratingmember driver by a harmonic spring/mass system.

FIG. 2C illustrates a displacement over time profile of an embodiment ofa controllable force driver.

FIG. 2D illustrates a velocity over time profile of an embodiment of acontrollable force driver.

FIG. 3 is a diagrammatic view illustrating a controlled feed-back loop.

FIG. 4 is a perspective view of a tissue penetration device havingfeatures of the invention.

FIG. 5 is an elevation view in partial longitudinal section of thetissue penetration device of FIG. 4.

FIG. 6 shows one embodiment of the present invention with a front endand landing a target tissue.

FIG. 7 are graphs showing tenting and force related to a lancing event.

FIG. 8-9 show schematics for a tissue penetrating device.

FIG. 10 shows a graph of tenting and penetration profiles.

FIGS. 11A-11G shows a method of penetrating tissue.

FIGS. 12A-12C show various embodiments of a tissue penetrating device.

FIGS. 13-15 show graphs of penetrating member velocity over time.

FIG. 16 shows a schematic representation of the reperfusion of skinafter impact.

FIG. 17 shows a tissue penetration device piercing skin.

FIGS. 18-21 are images of penetrating members and their interaction withtissue.

FIGS. 22-23 show various control methods as illustrated in graphs ofvelocity over time.

FIGS. 24-25 show schematics of embodiments of a penetrating memberdevice with a controller to account for pressure.

FIG. 26 shows a penetrating member in tissue.

FIG. 27 shows another embodiment of a slug for use with the presentinvention.

FIG. 28 shows a graph of force and displacement.

FIG. 29 shows a graph of electrical performance.

FIG. 30 shows a zero position for a solenoid driver.

FIGS. 31-43 show various graphs of penetrating member performance andcontrol schematics.

FIG. 44 shows a graph of penetrating member velocity versus time for oneembodiment of a control algorithm according to the present invention.

FIG. 45-46 shows one embodiment of a electronic drive mechanism.

FIGS. 47-53 show various graphs of penetrating member performance andcontrol schematics.

FIGS. 54-56 shows various embodiments of penetrating member drivers.

FIGS. 57 and 58 show graph of performance.

FIG. 59 shows one embodiment of disc for use with the present invention.

FIG. 60 shows one view of the disc in a penetrating member device.

FIG. 61 shows another embodiment of a device that may use a disc asdescribed in FIG. 59.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

The present invention provides a multiple analyte detecting membersolution for body fluid sampling. Specifically, some embodiments of thepresent invention provides a multiple analyte detecting member andmultiple penetrating member solution to measuring analyte levels in thebody. The invention may use a high density design. It may usepenetrating members of smaller size, such as but not limited to diameteror length, than known lancets. The device may be used for multiplelancing events without having to remove a disposable from the device.The invention may provide improved sensing capabilities. At least someof these and other objectives described herein will be met byembodiments of the present invention.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the invention, as claimed. It must be notedthat, as used in the specification and the appended claims, the singularforms “a”, “an” and “the” include plural referents unless the contextclearly dictates otherwise. Thus, for example, reference to “a material”may include mixtures of materials, reference to “a chamber” may includemultiple chambers, and the like. References cited herein are herebyincorporated by reference in their entirety, except to the extent thatthey conflict with teachings explicitly set forth in this specification.

In this specification and in the claims which follow, reference will bemade to a number of terms which shall be defined to have the followingmeanings:

“Optional” or “optionally” means that the subsequently describedcircumstance may or may not occur, so that the description includesinstances where the circumstance occurs and instances where it does not.For example, if a device optionally contains a feature for analyzing ablood sample, this means that the analysis feature may or may not bepresent, and, thus, the description includes structures wherein a devicepossesses the analysis feature and structures wherein the analysisfeature is not present.

The present invention may be used with a variety of differentpenetrating member drivers. It is contemplated that these penetratingmember drivers may be spring based, solenoid based, magnetic driverbased, nanomuscle based, or based on any other mechanism useful inmoving a penetrating member along a path into tissue. It should be notedthat the present invention is not limited by the type of driver usedwith the penetrating member feed mechanism. One suitable penetratingmember driver for use with the present invention is shown in FIG. 1.This is an embodiment of a solenoid type electromagnetic driver that iscapable of driving an iron core or slug mounted to the penetratingmember assembly using a direct current (DC) power supply. Theelectromagnetic driver includes a driver coil pack that is divided intothree separate coils along the path of the penetrating member, two endcoils and a middle coil. Direct current is alternated to the coils toadvance and retract the penetrating member. Although the driver coilpack is shown with three coils, any suitable number of coils may beused, for example, 4, 5, 6, 7 or more coils may be used.

Referring to the embodiment of FIG. 1, the stationary iron housing 10may contain the driver coil pack with a first coil 12 flanked by ironspacers 14 which concentrate the magnetic flux at the inner diametercreating magnetic poles. The inner insulating housing 16 isolates thepenetrating member 18 and iron core 20 from the coils and provides asmooth, low friction guide surface. The penetrating member guide 22further centers the penetrating member 18 and iron core 20. Thepenetrating member 18 is protracted and retracted by alternating thecurrent between the first coil 12, the middle coil, and the third coilto attract the iron core 20. Reversing the coil sequence and attractingthe core and penetrating member back into the housing retracts thepenetrating member. The penetrating member guide 22 also serves as astop for the iron core 20 mounted to the penetrating member 18.

As discussed above, tissue penetration devices which employ spring orcam driving methods have a symmetrical or nearly symmetrical actuationdisplacement and velocity profiles on the advancement and retraction ofthe penetrating member as shown in FIGS. 2 and 3. In most of theavailable lancet devices, once the launch is initiated, the storedenergy determines the velocity profile until the energy is dissipated.Controlling impact, retraction velocity, and dwell time of thepenetrating member within the tissue can be useful in order to achieve ahigh success rate while accommodating variations in skin properties andminimize pain. Advantages can be achieved by taking into account of thefact that tissue dwell time is related to the amount of skin deformationas the penetrating member tries to puncture the surface of the skin andvariance in skin deformation from patient to patient based on skinhydration.

In this embodiment, the ability to control velocity and depth ofpenetration may be achieved by use of a controllable force driver wherefeedback is an integral part of driver control. Such drivers can controleither metal or polymeric penetrating members or any other type oftissue penetration element. The dynamic control of such a driver isillustrated in FIG. 2C which illustrates an embodiment of a controlleddisplacement profile and FIG. 2D which illustrates an embodiment of athe controlled velocity profile. These are compared to FIGS. 2A and 2B,which illustrate embodiments of displacement and velocity profiles,respectively, of a harmonic spring/mass powered driver. Reduced pain canbe achieved by using impact velocities of greater than about 2 m/s entryof a tissue penetrating element, such as a lancet, into tissue. Othersuitable embodiments of the penetrating member driver are described incommonly assigned, U.S. patent application Ser. No. 10/127,395, filedApr. 19, 2002 (now U.S. Pat. No. 7,025,774, previously incorporatedherein.

In one embodiment, a controllable force driver is used to drive apenetrating member and can be powered by electromagnetic energy. Acontrollable driver can achieve a desired velocity versus positionprofile. The driver is coupled to a processor and a penetrating memberdriver to control depth of penetration, to control penetrating memberpenetration and withdrawal velocity, and therefore reduce the painperceived when cutting into the skin. Embodiments of the inventioninclude a controllable driver that can be used with a feedback loop witha position sensor to control the power delivered to the lancet, whichcan optimize the velocity and displacement profile to compensate forvariations in skin thickness.

The electromagnetic driver allows programmable control over the velocityvs. position profile of the entire lancing process including timing thestart of the lancet, tracking the lancet position, measuring the lancetvelocity, controlling the distal stop acceleration, and controlling theskin penetration depth.

In one embodiment, The electromagnetic driver has a moving partcomprising a lancet assembly with a penetrating member and amagnetically permeable flag attached at the proximal or drive end and astationary part comprising a stationary housing assembly with electricfield coils arranged so that they produce a balanced field at the flagto reduce or eliminate any net lateral force on the flag. The electricfield coils are generally one or more metal coils, which generate amagnetic field when electric current passes through the coil. The ironflag is a flat or enlarged piece of magnetic material, which increasesthe surface area of the penetrating member assembly to enhance themagnetic forces generated between the proximal end of the penetratingmember and a magnetic field produced by the field coils. The combinedmass of the penetrating member and the iron flag can be minimized tofacilitate rapid acceleration for introduction into the skin of apatient, to reduce the impact when the penetrating member stops in theskin, and to facilitate prompt velocity profile changes throughout thesampling cycle.

FIG. 3 illustrates the operation of a feedback loop using a processor60. The processor 60 stores profiles 62 in non-volatile memory. A userinputs information 64 about the desired circumstances or parameters fora lancing event. The processor 60 selects a driver profile 62 from a setof alternative driver profiles that have been preprogrammed in theprocessor 60 based on typical or desired tissue penetration deviceperformance determined through testing at the factory or as programmedin by the operator. The processor 60 may customize by either scaling ormodifying the profile based on additional user input information 64.Once the processor has chosen and customized the profile, the processor60 is ready to modulate the power from the power supply 66 to thepenetrating member driver 68 through an amplifier 70. The processor 60may measure the location of the penetrating member 72 using a positionsensing mechanism 74 through an analog to digital converter 76 linearencoder or other such transducer. Examples of position sensingmechanisms have been described in the embodiments above and may be foundin the specification for commonly assigned, U.S. patent application Ser.No. 10/127,395, filed Apr. 19, 2002 (now U.S. Pat. No. 7,025,774) andpreviously incorporated herein. The processor 60 calculates the movementof the penetrating member by comparing the actual profile of thepenetrating member to the predetermined profile. The processor 60modulates the power to the penetrating member driver 68 through a signalgenerator 78, which may control the amplifier 70 so that the actualvelocity profile of the penetrating member does not exceed thepredetermined profile by more than a preset error limit. The error limitis the accuracy in the control of the penetrating member.

In one embodiment, a penetrating member device includes a controllabledriver coupled to a penetrating member. The penetrating member devicehas a penetrating member coupled to an elongate coupler shaft by a drivecoupler. The elongate coupler shaft has a proximal end and a distal end.A driver coil pack is disposed about the elongate coupler shaft proximalof the penetrating member. A position sensor is disposed about aproximal portion of the elongate coupler shaft and an electricalconductor electrically couples a processor to the position sensor. Theelongate coupler shaft is driven by a driver coil pack, controlled bythe position sensor and processor coupled to the controllable driver,and by way of illustration and without limitation, a controllableelectromagnetic driver.

After the lancing event, the processor 60 can allow the user to rank theresults of the lancing event. The processor 60 stores these results andconstructs a database 80 for the individual user. Using the database 79,the processor 60 calculates the profile traits such as degree ofpainlessness, success rate, and blood volume for various profiles 62depending on user input information 64 to optimize the profile to theindividual user for subsequent lancing cycles. These profile traitsdepend on the characteristic phases of penetrating member advancementand retraction. The processor 60 uses these calculations to optimizeprofiles 62 for each user. In addition to user input information 64, aninternal clock allows storage in the database 79 of information such asthe time of day to generate a time stamp for the lancing event and thetime between lancing events to anticipate the user's diurnal needs. Thedatabase stores information and statistics for each user and eachprofile that particular user uses.

In addition to varying the profiles, the processor 60 can be used tocalculate the appropriate penetrating member diameter and geometrysuitable to realize the blood volume required by the user. For example,if the user requires about 1-5 microliter volume of blood, the processor60 may select a 200 micron diameter penetrating member to achieve theseresults. For each class of lancet, both diameter and lancet tipgeometry, is stored in the processor 60 to correspond with upper andlower limits of attainable blood volume based on the predetermineddisplacement and velocity profiles.

The lancing device is capable of prompting the user for information atthe beginning and the end of the lancing event to more adequately suitthe user. The goal is to either change to a different profile or modifyan existing profile. Once the profile is set, the force driving thepenetrating member is varied during advancement and retraction to followthe profile. The method of lancing using the lancing device comprisesselecting a profile, lancing according to the selected profile,determining lancing profile traits for each characteristic phase of thelancing cycle, and optimizing profile traits for subsequent lancingevents.

FIG. 4 illustrates an embodiment of a tissue penetration device, morespecifically, a lancing device 80 that includes a controllable driver179 coupled to a tissue penetration element. The lancing device 80 has aproximal end 81 and a distal end 82. At the distal end 82 is the tissuepenetration element in the form of a penetrating member 83, which iscoupled to an elongate coupler shaft 84 by a drive coupler 85. Theelongate coupler shaft 84 has a proximal end 86 and a distal end 87. Adriver coil pack 88 is disposed about the elongate coupler shaft 84proximal of the penetrating member 83. A position sensor 91 is disposedabout a proximal portion 92 of the elongate coupler shaft 84 and anelectrical conductor 94 electrically couples a processor 93 to theposition sensor 91. The elongate coupler shaft 84 driven by the drivercoil pack 88 controlled by the position sensor 91 and processor 93 formthe controllable driver, specifically, a controllable electromagneticdriver.

Referring to FIG. 5, the lancing device 80 can be seen in more detail,in partial longitudinal section. The penetrating member 83 has aproximal end 95 and a distal end 96 with a sharpened point at the distalend 96 of the penetrating member 83 and a drive head 98 disposed at theproximal end 95 of the penetrating member 83. A penetrating member shaft201 is disposed between the drive head 98 and the sharpened point 97.The penetrating member shaft 201 may be comprised of stainless steel, orany other suitable material or alloy and have a transverse dimension ofabout 0.1 to about 0.4 mm. The penetrating member shaft may have alength of about 3 mm to about 50 mm, specifically, about 15 mm to about20 mm. The drive head 98 of the penetrating member 83 is an enlargedportion having a transverse dimension greater than a transversedimension of the penetrating member shaft 201 distal of the drive head98. This configuration allows the drive head 98 to be mechanicallycaptured by the drive coupler 85. The drive head 98 may have atransverse dimension of about 0.5 to about 2 mm.

A magnetic member 102 is secured to the elongate coupler shaft 84proximal of the drive coupler 85 on a distal portion 203 of the elongatecoupler shaft 84. The magnetic member 102 is a substantially cylindricalpiece of magnetic material having an axial lumen 204 extending thelength of the magnetic member 102. The magnetic member 102 has an outertransverse dimension that allows the magnetic member 102 to slide easilywithin an axial lumen 105 of a low friction, possibly lubricious,polymer guide tube 105′ disposed within the driver coil pack 88. Themagnetic member 102 may have an outer transverse dimension of about 1.0to about 5.0 mm, specifically, about 2.3 to about 2.5 mm. The magneticmember 102 may have a length of about 3.0 to about 5.0 mm, specifically,about 4.7 to about 4.9 mm. The magnetic member 102 can be made from avariety of magnetic materials including ferrous metals such as ferroussteel, iron, ferrite, or the like. The magnetic member 102 may besecured to the distal portion 203 of the elongate coupler shaft 84 by avariety of methods including adhesive or epoxy bonding, welding,crimping or any other suitable method.

Proximal of the magnetic member 102, an optical encoder flag 206 issecured to the elongate coupler shaft 84. The optical encoder flag 206is configured to move within a slot 107 in the position sensor 91. Theslot 107 of the position sensor 91 is formed between a first bodyportion 108 and a second body portion 109 of the position sensor 91. Theslot 107 may have separation width of about 1.5 to about 2.0 mm. Theoptical encoder flag 206 can have a length of about 14 to about 18 mm, awidth of about 3 to about 5 mm and a thickness of about 0.04 to about0.06 mm.

The optical encoder flag 206 interacts with various optical beamsgenerated by LEDs disposed on or in the position sensor body portions108 and 109 in a predetermined manner. The interaction of the opticalbeams generated by the LEDs of the position sensor 91 generates a signalthat indicates the longitudinal position of the optical flag 206relative to the position sensor 91 with a substantially high degree ofresolution. The resolution of the position sensor 91 may be about 200 toabout 400 cycles per inch, specifically, about 350 to about 370 cyclesper inch. The position sensor 91 may have a speed response time(position/time resolution) of 0 to about 120,000 Hz, where one dark andlight stripe of the flag constitutes one Hertz, or cycle per second. Theposition of the optical encoder flag 206 relative to the magnetic member102, driver coil pack 88 and position sensor 91 is such that the opticalencoder 91 can provide precise positional information about thepenetrating member 83 over the entire length of the penetrating member'spower stroke.

An optical encoder that is suitable for the position sensor 91 is alinear optical incremental encoder, model HEDS 9200, manufactured byAgilent Technologies. The model HEDS 9200 may have a length of about 20to about 30 mm, a width of about 8 to about 12 mm, and a height of about9 to about 11 mm. Although the position sensor 91 illustrated is alinear optical incremental encoder, other suitable position sensorembodiments could be used, provided they posses the requisite positionalresolution and time response. The HEDS 9200 is a two channel devicewhere the channels are 90 degrees out of phase with each other. Thisresults in a resolution of four times the basic cycle of the flag. Thesequadrature outputs make it possible for the processor to determine thedirection of penetrating member travel. Other suitable position sensorsinclude capacitive encoders, analog reflective sensors, such as thereflective position sensor discussed above, and the like.

A coupler shaft guide 111 is disposed towards the proximal end 81 of thelancing device 80. The guide 111 has a guide lumen 112 disposed in theguide 111 to slidingly accept the proximal portion 92 of the elongatecoupler shaft 84. The guide 111 keeps the elongate coupler shaft 84centered horizontally and vertically in the slot 102 of the opticalencoder 91.

In another aspect of the present invention, this solution involves usingtwo measurements, tenting and force present at the front end of thelancing device 200, to interpolate the stratum corneum (SC) thickness atthat particular skin location. It is known that force applied to thefront end of a lancing device affects the amount of tenting caused by aninbound lancet. This effect can be visualized by plotting force vs.tenting on a linear scale. Varying Stratum Corneum thickness causes achange in the slope of this curve. This data can be used to interpolatean SC thickness value.

Referring now to FIG. 6, one embodiment of a lancing device 200 isshown. The arrow 202 indicates that a penetrating member will moveoutward to penetrate tissue. A finger (shown in phantom) will pressagainst the front end 204 which is coupled to a pressure transducer 206.This may in turn be coupled to a processor 208. The pressure transducer206 may be any one known in the art such as but not limited to a straingauge or a piezoelectric sensor. The processor 208 may be coupled tomemory M that stores readings.

Referring now to FIG. 7, experiment 342 shows that there are twodifferent slopes 220 and 222 for different SC thicknesses. Line 222corresponds to the thicker (313) SC while line 220 corresponds to thethinner (217) SC. Thus in the lancing device 200, by recording the force(which will undoubtedly vary) applied by the user and the tenting, theSC thickness can be determined based on the slope of the line. Methodsfor determining tenting are discussed in commonly assigned, copendingU.S. Pat. No. 7,141,058 may be used with the present invention. Itshould be understood that this information may be stored into thememory. The location used to lance may also be stored into memory M sothat measurements for specific sites may be grouped together.

It should be understood that the present invention relates to the waythat an electronically driven lancing device controls the trajectory ofthe inbound lancet up to the point of maximum extension. This is thepoint of maximum penetration of the lancet into the skin. In oneembodiment, the invention comprises a control algorithm, that whencombined with the suitable hardware to execute the control instructions,increases the depth accuracy. The present application also describes themethod of a quiet phase but only refers to traditional brakingadjustment after this phase. The present application also describes theidea of setting the contact velocity at a rate where coil activity isminimized and the control system “operates within a projectedtrajectory.”

Referring now to FIG. 8, one method of penetrating member control willbe described. The method of lancing starts with the penetrating membercontrol system 310 that is coupled to an electric drive mechanism 320used to accelerate the penetrating member 322 to a desired speed towarda target tissue T. The penetrating member 322 hits the skin at arelative point and then there is a switch when the penetrating member322 reaches a certain displacement. The control system will cause thebraking to come on. And then braking will happen really kind of anondeterministic way. The brakes are on, it goes to a certain depth.There is not an interactiveness with the control system as to where themember 322 is at, as to where it needs to be (from the point the brakingswitches on). The variance of where the member 322 is and where it wantsto be is could be improved.

Referring now to FIG. 9, with the present invention using one embodimentof what is termed “smart braking”, an adaptive control system 350 may beused to improve performance. Such a system 350 has the ability toredirect braking during the braking period to get to the member 322 tothe appropriate depth desired. In one embodiment, it is not necessarilya full-on braking up to the point of reversal in a binary manner (i.e.either full on or full off).

In one embodiment of adaptive control system 350, variable brakingforce, which is computationally more complex, may be used. In oneembodiment, for each duty cycle that the penetrating member 322 isbraking, the system 350 will look where the member 322 is, and where itshould be. There may be a look up table used to determine if the member322 is under or over the place where the member 322 wants to be for aparticular part of the braking cycle. The control system 350 canredirect or adjust braking (e.g. not as hard or harder in the nextbraking cycle). A position encoder 356 is used with the system 350.

In a still further embodiment of the present invention, a more complexprocessor may be used with the system 350. In this embodiment, ratherthan just a lookup table, the processor in control system 350 cancalculate the level of deceleration and maybe make that relative to thecontact point, so that you do not need to do an integration of thecurve. Instead of using a ton of lookup tables, the system 350 candirect the lancet with a more elegant algorithm.

In still other embodiments, the control system 350 may be paired with animproved position sensor. If the processor desires a certain amount ofdata to make a predictive decision within the braking segment, theamount of position feedback to the processor may be increased. It may bethat you may not have enough predictive ability because the controlsystem is limited or it comes too late. The penetrating member 322 mayalready have gone too far or the controller is too slow to make thechange. Accordingly, an improved position sensor may provide moreposition data. The data may arrive faster and it may be more precise asto the location of the penetrating member.

From an conceptual standpoint, it would be possible to further improvecontrol system performance. As discussed, the position encoder would beimproved. The clock speed of the processor would be faster to handle theadditional flow of data because it comes faster. Finer control of thesolenoid or other electronic drive mechanism may also be desired so thatsolenoid can move the penetrating member at a level of accuracy matchingor coming close to that of the position encoder.

Optimally, the present invention provides for controlling the trajectoryof the inbound lancet up to the point of maximum extension with anadaptive algorithm. With regards to the algorithm, in one embodiment,there is a decision point when the penetrating member 322 is stilltraveling in the inbound direction. With stored up data, based on thistime and this position and a desired depth or profile, the controlsystem 350 will make a decision whether to accelerate, brake, or donothing. The decision point will ultimately determine what depth thepenetrating member 322 reaches. It should be understood of course thatthere may be more than one decision point in a braking cycle. But if thedeceleration is too high or other factors excessively slow the member322, the control system 350 may choose to accelerate rather than brake.It could also brake harder, as the circumstances warrant.

It should also be understood that it may be possible to bring down thevariance where the lancet ultimately ends up. For a certain depth, thereis an optimal contact speed, given the uncertainly once the penetratingmember 322 goes past initial contact with the tissue. It helps that theentire control system, in that it gives a neutral composition. There maybe some braking or some acceleration, but there is not a huge amount ofcorrection. There is a neutral position.

In one embodiment, if the braking algorithm is more complex in the sensethat instead of just looking at position and time, it is looking atposition and time for the last three cycles and dividing that into asmooth braking factor and taking that's distance (or corrected distancebased on the contact point routine), then it is a simple multiplicationof this factor and that position factor and that the system does notneed a true update at the next look up table interval. It is a rollingaverage that gets the penetrating member to the intended depth at ahigher degree of accuracy.

There is some variability with how the skin performs. Physiologically,as a nonlimiting example, a stick of about 2 mm in depth might increasethe actual depth by +/−300 microns. Even though theoretically, thesystem can get really close to the desired depth with the controlsystem, other mechanical or physiological reasons may create errors.Smarting braking increase the stability of the control system. It mighthave a more stable profile to deal with physiological uncertainties thatare otherwise unaccounted for.

Various velocity profiles can influence cutting efficiency and morespecifically, a final depth as the tissue reacts differently based onvelocity of the penetrating member. As a nonlimiting example, if thepenetrating members goes in fast and is braked hard, the tissue maystill have momentum and the tissue/lancet interface may not be stable(i.e. not move together), and it might end up being that the compositionof the tissue plays more of a factor. If you had a more stable control,the physiological variability of the tissue could be reduced orsubstantially taken out of the equation. In one embodiment of thepresent invention, the control tends to adjust the braking cycle so thatthe rate of deceleration is relatively constant and keeps the tissue orskin in a state where it does not have any unfair loads put on it. Ifthe braking occurs too suddenly, the skin can bound away from the lancetand be keep moving.

Other improved embodiments of the control system, in addition toaccounting for position and velocity, they may also account fortrajectory. In one embodiment, the ideal lancing algorithm involvesdriving the lancet at a high rate of velocity to a predetermined depth,stopping at a given distance, and pulling out the lancet at a givenrate. By achieving a contact speed, the device can meter the amount offorce it presents to the skin at impact. This contact speed will behigher for a lancing cycle in which a higher penetration depth isintended. A velocity lookup table corresponding to the composite amount(The average velocity necessary to achieve a certain depth throughiteration of many sticks) is set as one of the directions to the controlsequence. The decision to redirect the lancet should come late in thelancing cycle and should be relative to displacement, rather thanvelocity. If the lancet passes within a certain distance of the intendeddisplacement, the velocity can be checked by the control processor, andcompared to a velocity lookup table.

As a nonlimiting example, 0.5 millimeters before the intendedpenetration distance, the speed is 30% of the contact speed. Accordingto the velocity lookup table that is stored for this control algorithmand called at this displacement, the speed should be 30%. In this case,the control system does nothing to redirect the lancet. If the speed was20% of the contact speed, this would indicate to the device that thelancet had decelerated too much, and a metered burst of energycorresponding to its deviation would be applied to the lancet from thedrive motor to accelerate lancet to its intended displacement. If thespeed was 40% of the contact speed, the lancet would be decelerated witha metered burst of energy. Because a linear position sensor has betterposition/time resolution at higher speeds and the ability of the motorto accelerate or decelerate is higher at low speeds, the decision toaccelerate or brake should come at a displacement in which the velocityis consistently within the optimal working range of the position encoderand the motor. It should also occur late enough in the lancing cycle tobe predictive. There may be more than one position-based decision pointwhile penetrating, but the processing speed, force response of theelectronic motor, and resolution of the position sensor are the physicaldeterminants of whether this is feasible for the system and within whatrange of positions this control methodology is effective.

A more complex control algorithm would also utilize a least squaresmethod in tandem with the velocity and position comparison. In thisembodiment, this binomial equation would determine the rate ofdeceleration and invoke the braking or acceleration algorithm with theadditional factor concerning the shape of the curve. It woulddistinguish between skin stiffness and skin position by effectivelyintegrating the velocity vs. position curve during the decelerationphase of the lancing cycle. An algorithm factors these variables andaccounts for them during in the control loop will provide a moredesirable result, in terms of cutting efficiency and desired penetratingdepth of a penetrating member into tissue.

In yet another embodiment of the present invention, disclosure isprovided herein that relates to a mode of operation with an electroniclancet drive system where the inbound penetration of the lancet to theskin is determined by the amount of force applied by the motor.Referring now to FIG. 10, the graph shows lancing sticks or events intothe same finger with different contact speeds. As seen in FIG. 10, thereis a strong correlation between speed and penetration. No feedback isapplied to obtain a certain position. As seen in FIG. 10, therepeatability of the depth appears to be high. There is also arelatively predictable way that the skin tents above a certain speed.

The current method concerning lancing involves driving the lancet at ahigh rate of velocity to a predetermined depth, stopping at a givendistance, and pulling out the lancet at a given rate. In the presentembodiment of the invention, the system involves an alternative controlmode of operation where the intended depth is not held constant.

With electronic lancing and position feedback, the lancing device 20 canmeter the amount of force it presents to the skin at impact. The contactspeed will be higher for a lancing cycle in which a higher penetrationdepth is intended. In one embodiment, a velocity lookup tablecorresponding to the composite amount (the average velocity necessary toachieve a certain depth through iteration of many sticks) is set as oneof the directions to the control sequence. There may be a desire not toexceed threshold of a certain position in which the lancet controlsystem intervenes and stops the lancet from penetrating further.

The tenting and penetration appeared to be more consistent than whenfeedback is applied. When the rate of a blade already cutting through amaterial is suddenly changed, the cutting efficiency decreases and theblade binds. This may translate into increases in the amount andvariance of deflection, or tenting, of the skin.

It should understood that this type of setup may be advantageous modefor some users. This is true if the physiological characteristics thatdetermine successful sampling hold more consistently with force appliedrather than depth achieved. Successful sampling is defined as asufficient sample with a minimum of pain. The control system canintroduce uncertainty for certain types of sticks by providing aposition-based correction that does not need to occur. The device is notlimited to this forced-based mode. Both force and position based controlmay be loaded on the same device.

Fixed Contact Point

Referring now to FIGS. 11A-11G, in one embodiment, the processordetermines that the skin has been contacted when the end tip of thepenetrating member has moved a predetermined distance with respect toits initial position. If the distance from the tip 961 of thepenetrating member 183 to the target tissue 233 is known prior toinitiation of penetrating member 183 movement, the initial position ofthe penetrating member 183 is fixed and known, and the movement andposition of the penetrating member 183 can be accurately measured duringa lancing cycle, then the position and time of penetrating membercontact can be determined. This method requires an accurate measurementof the distance between the penetrating member tip 196 and the patient'sskin 233 when the penetrating member 183 is in the zero time or initialposition. This can be accomplished in a number of ways. One way is tocontrol all of the mechanical parameters that influence the distancefrom the penetrating member tip 196 to the patient's tissue or a surfaceof the lancing device 180 that will contact the patient's skin 233. Thiscould include the start position of the magnetic member 202, magneticpath tolerance, magnetic member 202 dimensions, driver coil pack 188location within the lancing device 180 as a whole, length of theelongate coupling shaft 184, placement of the magnetic member 202 on theelongate coupling shaft 184, length of the penetrating member 183 etc.If all these parameters, as well as others can be suitably controlled inmanufacturing with a tolerance stack-up that is acceptable, then thedistance from the penetrating member tip 196 to the target tissue 233can be determined at the time of manufacture of the lancing device 180.The distance could then be programmed into the memory of the processor193. If an adjustable feature is added to the lancing device 180, suchas an adjustable length elongate coupling shaft 184, this canaccommodate variations in all of the parameters noted above, exceptlength of the penetrating member 183. An electronic alternative to thismechanical approach would be to calibrate a stored memory contact pointinto the memory of the processor 193 during manufacture based on themechanical parameters described above.

In another embodiment, moving the penetrating member tip 196 to thetarget tissue 233 very slowly and gently touching the skin 233 prior toactuation can accomplish the distance from the penetrating member tip196 to the tissue 233. The position sensor can accurately measure thedistance from the initialization point to the point of contact, wherethe resistance to advancement of the penetrating member 183 stops thepenetrating member movement. The penetrating member 183 is thenretracted to the initialization point having measured the distance tothe target tissue 233 without creating any discomfort to the user.

Using an Acoustic Signal to Determine Contact Point

In yet another embodiment, the processor 193 determines skin 233 contactby the penetrating member 183 by detection of an acoustic signalproduced by the tip 196 of the penetrating member 183 as it strikes thepatient's skin 233. Detection of the acoustic signal can be measured byan acoustic detector 236 placed in contact with the patient's skin 233adjacent a penetrating member penetration site 237, as shown in FIG. 31.Suitable acoustic detectors 236 include piezo electric transducers,microphones and the like. The acoustic detector 236 transmits anelectrical signal generated by the acoustic signal to the processor 193via electrical conductors 238.

Using Continuity in an Electric Circuit to Measure Contact Point

In another embodiment, contact of the penetrating member 183 with thepatient's skin 233 can be determined by measurement of electricalcontinuity in a circuit that includes the penetrating member 183, thepatient's finger 234 and an electrical contact pad 240 that is disposedon the patient's skin 233 adjacent the contact site 237 of thepenetrating member 183. In this embodiment, as soon as the penetratingmember 183 contacts the patient's skin 233, the circuit 239 is completedand current flows through the circuit 239. Completion of the circuit 239can then be detected by the processor 193 to confirm skin 233 contact bythe penetrating member 183. If the penetrating member 183 has notcontacted the target skin 233, then the process proceeds to a timeoutoperation. In the timeout operation, the processor 193 waits apredetermined time period. If the timeout period has not yet elapsed (a“No” outcome from the decision box 267), then the processor continues tomonitor whether the penetrating member has contacted the target skin233. The processor 193 preferably continues to monitor the position andspeed of the penetrating member 183, as well as the electrical currentto the appropriate coil 214-217 to maintain the desired penetratingmember 183 movement. If the timeout period elapses without thepenetrating member 183 contacting the skin (a “Yes” output from thedecision box 267), then it is deemed that the penetrating member 183will not contact the skin and the process proceeds to a withdraw phase,where the penetrating member is withdrawn away from the skin 233, asdiscussed more fully below. The penetrating member 183 may not havecontacted the target skin 233 for a variety of reasons, such as if thepatient removed the skin 233 from the lancing device or if somethingobstructed the penetrating member 183 prior to it contacting the skin.

Reduction in Penetrating Member Velocity to Determine Contact Point

In another embodiment, the processor 193 may use software to determinewhether the penetrating member 183 has made contact with the patient'sskin 233 by measuring for a sudden reduction in velocity of thepenetrating member 183 due to friction or resistance imposed on thepenetrating member 183 by the patient's skin 233. The optical encoder191 measures displacement of the penetrating member 183. The positionoutput data provides input to the interrupt input of the processor 193.The processor 193 also has a timer capable of measuring the time betweeninterrupts. The distance between interrupts is known for the opticalencoder 191, so the velocity of the penetrating member 183 can becalculated by dividing the distance between interrupts by the timebetween the interrupts. This method requires that velocity losses to thepenetrating member 183 and elongate coupler 184 assembly due to frictionare known to an acceptable level so that these velocity losses andresulting deceleration can be accounted for when establishing adeceleration threshold above which contact between penetrating membertip 196 and target tissue 233 will be presumed.

This same concept can be implemented in many ways. For example, ratherthan monitoring the velocity of the penetrating member 183, if theprocessor 193 is controlling the penetrating member driver in order tomaintain a fixed velocity, the power to the driver 188 could bemonitored. If an amount of power above a predetermined threshold isrequired in order to maintain a constant velocity, then contact betweenthe tip of the penetrating member 196 and the skin 233 could bepresumed. All of the above figures are in reference to figures found inU.S. patent application Ser. No. 10/127,395 (now U.S. Pat. No.7,025,774).

Using a Slow Moving Penetrating Member to Determine Contact Point

In a still further embodiment, a new contact point algorithm is runbefore the actual lance event. As a nonlimiting example, such analgorithm may be run immediately prior to lancing.

Whether the penetrating member is striking a finger or othermaterial/object can be determined. Information about the skin propertiesof the finger can be determined. With a reasonable sized aperture, thefinger contact point can vary by more than the depth of penetration.Unless the contact point can be accurately determined, correct depth maybe difficult to control. This method cancels out mechanical variationsthat occur in the manufacturing process of the actuator, coupling to thepenetrating member, and length of the penetrating member. In addition,we can determine if there is anything there at all (strike into air).The finger in the above description can be any part of the body to belanced.

Description of the algorithm: In one embodiment, the penetrating memberis accelerated to a slow speed, in the present embodiment of theactuator, it is about 0.6 to 0.8 meters/second. It should be understoodthat this is a nonlimiting example. The speed may be tuned to the massof the lancing assembly. The more the mass of the assembly, the slowerthe speed should be. Since the energy stored in the assembly isdetermined by ½ MV², the desire is to store a sufficiently small amountof energy such that the penetrating member does not penetrate or doesnot significantly penetrate the stratum corneum of the skin.

Referring now to FIG. 12A-12C, the speed of the penetrating member ismaintained at the desired velocity until the Start Contact Search Point400 is reached. In the present embodiment, this is simply first pointbefore the contact can occur. The coil power is turned off when theStart Contact Search Point is reached, and the penetrating memberassembly coasts. In one embodiment, this Start Contact Search Point maybe where the front end of the device is located.

Unimpeded, the penetrating member assembly in this present embodiment ofthe invention will coast until the Stop Contact Search Point is reached402. In the present embodiment, this is simply the maximum point atwhich a finger can be placed for a valid strike to be achieved. Sincethe penetrating member assembly has a maximum depth limited by thephysical stop, unless there is enough depth available (maximumdepth-contact point has to be >desired depth) there is no reason tocontinue the stick. This is also the way it is determined that thepenetrating member would strike into air.

While coasting, a base speed of the penetrating member at the beginningof the Start Contact Search Point is established and the speed of thepenetrating member assembly is monitored. Position feedback andmonitoring is discussed in commonly assigned U.S. patent applicationSer. No. 10/127,395 filed Apr. 19, 2002 (now U.S. Pat. No. 7,025,774),fully incorporated herein by reference. When a slowdown of more than apreset threshold (in one embodiment, we have found that about 12.5%seems to work fine), the distance at which this occurs is recorded. Inone embodiment, this distance may be recorded in the processor or inmemory coupled to a processor. This is called the tentative contactpoint 404. Using a quadrature phase sensor in one embodiment of thepresent invention or other sensor, we can measure direction. Thecoasting continues until a reversal of direction or a timeout occurswith no reversal. In one embodiment, if no reversal occurs, we mayassume that either binding in the mechanical assembly occurred or thepenetrating member struck something that did not rebound. This is calleda stall.

The penetrating member and driver are configured so that feedbackcontrol is based on penetrating member displacement, velocity, oracceleration. The feedback control information relating to the actualpenetrating path is returned to a processor that regulates the energy tothe penetrating member driver, thereby precisely controlling thepenetrating member throughout its advancement and retraction.

If a reversal of direction occurs, we store this value or distance too.The difference between the reversal point 406 and tentative contactpoint 404 is calculated. The positions shown in FIG. 12A purelyillustrative and are nonlimiting. If the difference is lower than apreset threshold, we know this is not a typical finger. If thedifference is above the threshold we declare it is a finger and thedifference between the two is a measure of the stretching or tenting asdiscussed in U.S. patent application Ser. No. 10/127,395 (now U.S. Pat.No. 7,025,774) or U.S. Pat. No. 7,141,058. In one embodiment, the aboverules result in many output codes from the contact point algorithm. Theyare summarized below.

Valid Contact Point Detected (Outputs Contact Point Measurement andReversal Point)

Stop Contact Search Point exceeded. No contact point detected becausethere was no slowdown within the Contact Search range (Start ContactSearch Point to Stop Contact Search Point).

Start Contact Search Point error. The contact point (slowdown) wasdetected too close to the Start Contact Search Point such that theslowdown might have already started during the establishment of the basespeed.

Stall—A stall is an error that results from a slowdown detected, but noreversal (described above).

Contact Hard Surface—this error results from a the difference betweenthe reversal and tentative contact point being is lower than a presetthreshold. This indicates the object hit did not deform, so we know thisis not a typical finger.

The difference between the threshold value and the actual measureddifference between the reversal point 406 and the tentative contactpoint 404 may be used to adjust the desired penetration depth. Forexample, if the distance between points 406 and 404 is greater than athreshold value, then this tissue exhibits more tenting than thestandard tissue model. The desired penetration depth may then beincreased to account for the extra tenting. On the other hand, if itturns out that the distance between points 406 and 404 is less than thethreshold, then this tissue exhibits less tenting. The desiredpenetration depth may then be reduced, by a proportional amount in oneembodiment, since the tissue has less tenting to account for.

After the skin or other tissue relaxes, the difference between thereversal position 406 and the initial position 404 may be measured sothat the amount of tenting T for this stick or lancing event is known.Now the actual penetration or depth in the skin or tissue may becalculated and a new target depth may be calculated by adding thevariance of the actual depth from that of the threshold to the targetdepth to yield a new target depth that now compensates for the amount oftenting. In one embodiment, the engine or penetrating member driver thatactuates the penetrating member is reengaged to achieve the new targetdepth which includes the distance to compensate for tenting. Thisprocess is relatively fast such as but not limited to under about 50 ms,so that it appears and feels like one operation to the user or patient.In another embodiment, at least one separate probe may be used toprovide skin qualities. As a nonlimiting example as seen in FIG. 12B, aseparate probe 410 with mass and dimension substantially similar to thatof the penetrating member 412 may be used to determine tissue quality.The probe 410 may be used to determine features and then the penetratingmember 412 fired to create the tissue wound. In another embodiment, acoaxially mounted movable probe (slidable over the penetrating member)may be advanced to determine tissue quality.

In another aspect of the present invention, penetration depth may becontrolled via speed and deceleration power modulation. Penetrationdepth of an electronically actuated penetrating member device iscontrolled by modulating the speed and the deceleration power. In otherembodiments, the methodology was to accelerate the penetrating member toa constant speed and control depth by adjusting the point along thepenetrating member trajectory where braking began. This currentembodiment of the method takes advantage of the ability to modulate theamount of braking power applied as well as the ability to modulatepenetrating member speed to control penetration depth. Penetratingmember speed has also been studied and optimized for each depth setting.Varying the braking power provides a still further variable which may beadjusted to provide improved penetration depth control. It may alsoallow for more variety in velocity profiles used with actuating thepenetrating member.

Referring to FIG. 13, as a nonlimiting example, being able to increasethe braking force allows a user to increase penetration velocity andmaintain that velocity for a longer period of time in the tissue andthen bring the penetrating member to a stop a the desired depth. Inother embodiments as seen in FIG. 14, it may be desirable to brakeslowly over a greater distance and thus provide a soft stop. In a yetfurther embodiment as seen in FIG. 15, the braking force may bemodulated to be any combination of the above such as but not limited toan initial hard braking followed by a period of soft braking to bringthe penetrating member to a controlled stop. It should be understoodthat any combination of the above hard and soft braking may be used.Variation in braking force also provides an additional variable duringfeedback control such that position of the penetrating member as itnears a desired depth may be braked with more force so that thepenetrating member stops at the desired depth. It should be understoodthat the above may be used with an electronic lancing device asdisclosed in U.S. patent application Ser. No. 10/127,395 (now U.S. Pat.No. 7,025,774). The braking force control may be adapted for use with aprocessor. The braking force control may be used with a multiplepenetrating member device such as that disclosed in U.S. PatentApplication 60/476,584.

Referring now to FIG. 16, a schematic representation of the reperfusionof skin after impact with a tent and hold motion profile is shown. Thisfigure is not to scale, and does not describe depth. This is a top downschematic view onto the skin or tissue. Penetrating member strikesperpendicularly to the skin in area A. Blood is initially forced out toan area D. Blood will quickly return from D to C as the skin settlesafter the shock of impact. Tent and hold allows blood reperfusion from Cto B and is due to the delayed deformation of the skin tissueimmediately around A, unloading the peripheral skin tissue vasculature.The vasculature also functions as a pressure system, forcing bloodtowards the penetrating member after a delay that is related to theforce of impact. This pressuring is one factor in increasing spontaneousblood generation.

Referring now to FIG. 17, two components of retraction profile areshown: As a nonlimiting example, reference letter A shows a“hold-to-neutral” position or range—when skin-penetrating memberinterface migrates together, and the skin settles naturally after theimpact force tents the tissue. Perfusion acts as three-dimensionalfunction of the pressure. Pressure distribution and perfusion iscone-shaped, as illustrated by the blue triangle below. Reference letterB shows neutral to exit position or range where the actuator retractsthe penetrating member from the skin.

Referring now to FIG. 18, a high resolution image of the penetratingmember and skin interface is shown. Specifically, the figure shows a“hold-to-neutral” phase-when skin-penetrating member interface migratetogether.

Referring now to FIG. 19, a high-resolution optical image of skinrelaxation “Natural Settling” with skin relaxing unimpeded bypenetrating member.

In some embodiment, a tent and hold profile 1 at 2.6 ms may be used. Atent and hold profile 1 at 6.6 ms is used in some embodiments. Primaryvisible skin buckling has broadened, and proximal edge of the woundchannel has slid up the penetrating member shaft. A tent and Holdprofile 2 at 3.9 ms is shown. Other experiment parameters are heldconstant. A tent and hold profile 2 at 6.6 ms is shown. The buckling isnot as evident, but the sliding is more obvious.

Referring now to FIG. 20, a Natural relaxation 4 seconds after thestrike is shown. After a good initial spontaneous flow, the flow stalls.

Referring now to FIG. 21, a Tent and Hold profile 2 at 4 s is shown. Themotion profile results in an extended period of high spontaneous flow.Module fills despite large offset of the skin relative to the collectionchannel.

Spontaneous blood yield can be achieved by a lancing motion profile thatholds the penetrating member at maximum extension for a prolonged periodof time. The viscoelastic of the skin may allow for a momentary tissuedeflection that would rebound immediately after the penetrating memberwas retracted. A tent and hold lancing profile counteracts this naturalproperty of the skin. In one embodiment, the penetrating member drivercan maintain an extended position for about 2-8 ms, and then make acontrolled retraction out of the finger. The skin will slide up thepenetrating member shaft as the collagen matrix in the reticular layerinelastically deforms. In this nonlimiting example, the penetratingmember continues to cut, but only as a result of the relaxation of thesurrounding tissue. This deformation during the hold happens radially aswell as axially to the penetrating member shaft. With tissue compressedmore evenly around the lanced area, the resulting wound maintains itshape longer before it collapses into a thin line that would resistblood spontaneously rising to the surface. The wound shape may exhibitincreased blood sufficiency by counteracting tissue reboundcharacteristics using the tent and hold profile.

In one embodiment, to achieve a “tent-and-hold” event, the penetratingmember penetrates to the intended depth and then may maintain theposition in the skin to prevent or retard the relaxation of the tissue,which would naturally return at approximately 1 m/s. In one nonlimitingexample, holding the penetrating member in the skin between about 2 to100 milliseconds appears be ideal to achieve spontaneous blood yield.Deeper lances will require more “hold” time. In one embodiment, hold maybe achieved by removing the drive force from the penetrating memberwhile letting the skin or tissue relax and reposition the penetratingmember. In other embodiments, hold may involve placing the penetratingmember at a fixed depth and maintaining that depth for the desiredperiod. Although not limited by the following, motion profiles for whichthe hold time is longer than about 1 second may introduce a deleteriousphysical reaction from the patient or unnecessary pain. It may also usemore power from the motor to maintain the position of the penetratingmember for an extended period of time.

Some advantages of a “tent-and-hold” motion profile or trajectorywaveform include:

Integrity of the wound channel by decreasing the effect of distension inthe wound channel. The viscoelasticity of the skin may allow for amomentary tissue deflection that would rebound immediately after thepenetrating member was retracted. A tent and hold lancing profile maycounteract this natural property of the skin. This behavior can bedirectly observed when the penetrating member is held for greater than200 microseconds. The skin will slide up the penetrating member shaft asthe collagen matrix in the stratum reticulare layer inelasticallydeforms. The penetrating member continues to cut, but only as a resultof the relaxation of the surrounding tissue. This deformation during thehold happens radially as well as axially to the penetrating membershaft. With tissue compressed more evenly around the lanced area, theresulting wound maintains it shape longer before it collapses into athin line, which may resist blood spontaneously rising to the surface.

A limited amount of pinching and subsequent binding of the venuoles (atdeeper lancing depths) by surrounding tissue at the target depth. In onenonlimiting example, a strike with the best yield would involve thelarger venuoles at higher depths filling the channel with blood. As theblood moves with the retracting penetrating member up the channel, theinside of the channel is coated with blood, allowing the blood insmaller venuoles with higher pressures to overcome to use the advantageof the bloods natural surface tension to lower the pressure thresholdthat would prevent blood spontaneously coming to the surface. Themomentum that a well-executed tent and hold with an appropriateretraction rate would build in the lancing channel not only decreasesthe number of sticks or lancing events with no spontaneous blood, butdecrease the number of spontaneous sticks that are spontaneous but wouldrequire milking of the finger to gather a sufficient sample. Thisincrease in the yield/depth ratio would thereby reduce pain/yield, as anoptimal retraction speed profile would reduce the depth sufficient togather a sufficient sample.

The force of the impact evacuates the blood from the area around thepenetrating member channel. This lack of movement after the impactallows for reperfusion into the area of the strike before anysignificant movement occurs. If the pressure is too high in the tentedtissue area, the blood may not return until the retraction is performed.However, the coherence and focus of the tissue reperfusion is greaterwith the device-controlled relaxation of the penetrating member.

Once the penetrating member holds a certain period of time, there aretwo components of the retraction profile that influences bloodspontaneously reaching the surface of the skin. The held-to-neutralsubcomponent, (which may be at a speed), which facilitates a focused andoptimal reperfusion of the lanced area; and the neutral-to-exitsubcomponent, which allows the penetrating member to perform at leastone of the following:

Travel without Binding or Damaging the Wound Channel.

Prevent the channel from closing up abruptly, enabling blood to displacethe penetrating member as it performs a controlled exit.

The power requirement to hold a penetrating member may vary. Variationsmay be due in part to type of drive device such as but not limited tosolenoid or voice coil and the like. In another embodiment, thepenetrating member may apply a force only great enough to slow therelaxation of the skin, but not to hold the relaxation of the skin. Therelationship of the power to tent-and-hold, or damp-and-hold may berelated to: the skin characteristics e.g. hydration, possibly stratumcorneum thickness. The power used to retract the penetrating member froma given depth or given skin may be used to relate characteristics of theskin. The wound stabilization characteristics required to get the bloodout, reorientation of collagen fibers to keep the channel patent, maydepend on the velocity profile used.

Some of the various embodiments of motion profiles, velocity profiles,or velocity waveforms are shown in FIGS. 22A-22C. As a nonlimitingexample, FIG. 22A shows a velocity versus time chart for a tent and holdvelocity profile. After the hold period 500 where sufficient force isapplied to hold the penetrating member at the current depth in thetissue, in this embodiment, there is a withdrawal phase 502 where thepenetrating member is backed out of the tissue at a velocity slower thatthe average entry velocity. The portion 502 is for velocity on thewithdrawal of the penetrating member from the tissue.

Referring now to FIG. 22B, another embodiment of the velocity profile isshown. In this embodiment, the profile is characterized as a “tent anddamped hold” where sufficient force is applied to the penetrating memberto allow it to move retrograde, but at a velocity slower than that whichit would move if no force were applied and the skin or tissue naturallyrelaxes. The damped hold over region 502 may occur at a controlled rate.After this damped hold, the penetrating member may be backed out of theskin at reduced velocity as indicated by 502.

Referring now to FIG. 22C, yet another embodiment of a velocity waveformis shown. FIG. 22C shows an embodiment where there is a hold period 500,after which the penetrating member is withdrawn using a steppedwithdrawal. In one nonlimiting example, the steps occur so that theaverage withdrawal speed is less that the average penetrating memberinbound speed. The stepped configuration may provide more time forcollagen in the skin to form around the shaft of the penetrating memberduring each withdrawal motion so that the wound shape and patentness ofthe wound channel may be maintained more easily (temporarily) by thecollagen. This allows body fluid to more easily follow the wound tractcreated by the penetrating member so that the fluid can reach thesurface. The steps may be at various spacings such as but not limited toabout 50 ms per step, 75 ms per step, 100 ms per step, or other steptimes as desired.

Referring now to FIG. 22D, a still further embodiment of the waveform isshown. FIG. 22D shows a profile where the hold period 500 is of anextended time. This may allow the collagen to form about the penetratingmember to help maintain the patentency of the wound channel. After aselectable amount of time, the penetrating member may be backed out ofthe skin as indicated by 512. The embodiment shown in FIG. 22D has thepull out occurring at an average velocity greater than that of theaverage inbound penetrating member velocity. In one embodiment, theoverall time that the penetrating member is in the tissue may be about500 ms. In other embodiments, the overall time in tissue or skin may beabout 450 ms, 400 ms, 350 ms, 300 ms, 250 ms, 200 ms, 150 ms, 100 ms, 75ms, 50 ms, 25 ms, 20 ms, or 15 ms. These number may be applicable to anyof the velocity profiled disclosed herein or in the profiles shown inU.S. patent application Ser. No. 10/127,395 (now U.S. Pat. No.7,025,774).

FIG. 23 shows an embodiment where it should be understood thepenetrating member velocity may be increased or decreased or maintainedbased on various decision points along the velocity trajectory. Furtherdisclosure can be found in commonly assigned, copending U.S. patentapplication Ser. No. 10/420,535 filed Apr. 21, 2003, and fullyincorporated herein by reference.

Referring now to FIG. 24, a still further embodiment, a controller mayalso account for pressure from applying a front end of the body fluidsampling device to the skin or tissue. The effect of front end pressureand stretching are discussed in U.S. Pat. No. 6,306,152 fullyincorporated herein by reference. Stretching from the front end mayinfluence the amount of tenting of the underlying tissue. In oneembodiment, the front end 560 may have an aperture sized of about 4.5mm. The aperture may be varied in size from annular ring, square,triangular, polygonal, hexagonal, or other shaped. In one embodiment,the front end 560 may be movable into the housing as seen in FIG. 25.The front end 560, when depressed, may configured to only provide aselected amount of force, thus making the tenting quality of the skinmore controllable. In other embodiments, a pressure transducer 562 maybe coupled to the front end. The measurements from the pressuretransducer 562 may be used by the controller 564 to adjust the tentingadjustment. Various adjustment amounts may be stored in a lookup tablein the device. The pressure transducer 562 may also be used duringcalibration or measurement of the tenting T so that it will be recordedand adjusted for if later lancings with the device do not occur at thesame pressure. The tenting amount T may be adjusted based on thepressure used during the original measurement and the amount beingapplied during the current lancing.

In a still further embodiment of the present invention, a method foraccurate control of penetrating member depth will be discussed.Referring now to FIG. 26, the invention claims that the true depths maybe consistently obtained for a desired depth by lancing to the desireddepth neglecting tenting. In one embodiment, after this first depth 530is achieved, the drive is turned off and skin or other tissue is allowedto relax until it has a neutral or “un-tented” as shown in FIG. 17 andper previously described in commonly assigned, U.S. patent applicationSer. No. 10/127,395 filed Apr. 19, 2002 (now U.S. Pat. No. 7,025,774),and incorporated herein by reference. In FIG. 14, this position is shownat position 532.

After the skin or other tissue relaxes, the difference between thedeepest penetration to position 530 and the relaxed position 532 may bemeasured so that the amount of tenting T for this stick or lancing eventis known. Now the actual penetration or depth in the skin or tissue maybe calculated and a new target depth may be calculated by adding thetenting distance T to the target depth to yield a new target depth thatnow compensates for the amount of tenting (assuming the position 530represented the desired depth of penetration into tissue. In oneembodiment, the engine or penetrating member driver that actuates thepenetrating member is reengaged to achieve the new target depth whichincludes the distance to compensate for tenting. This process isrelatively fast such as but not limited to under about 50 ms, so that itappears and feels like one operation to the user or patient.

In other embodiments, once the tenting T is calculated, the tentingamount T may be used for subsequent lancing events. A penetrating membercontroller (not shown) may include or be coupled to memory that willstore this tenting distance. Thus, subsequent lancing events may beconfigured to account for the tenting distance on the first inboundstroke and achieve a desired depth without necessarily using a truedepth type penetration stroke on each lancing event. Thus the depth forpenetrating member penetration will include a desired depth D and thetenting T. The calculation of tenting T may be initiated on a firstlancing event by the user and on any subsequent lancing events asdesired by the user for recalibration of tenting purposes. In stillfurther embodiments, the tenting distance T may also be adjusted by acertain amount (such as but not limited to ±1%, ±2%, ±3%, ±4%, ±5%, ±6%,±7%, ±8%, ±9%, ±10%, or more) based on the time of day and hydrationpattern of the user or patient. A lookup table containing differenttenting distances T may also be used to pick off the desired amount oftenting compensation based on a number of variables such as but notlimited to: time of day, hydration, age of patient, or other patientinformation.

In some embodiments, the penetrating member on the inbound pathpenetrates into the tissue during the tenting measurement. In otherembodiments, the penetrating member does not fully pierce the patientwhile gathering information of tenting distance.

Referring now to FIGS. 27 and 28, further embodiments of the presentinvention will now be described. These embodiments relate tomodifications for the electronic drive mechanisms used with the presentinvention.

Solenoid Study

The objective of the solenoid study is to further understand itsoperation and to look for techniques to further enhance the forcecapability. The existing solenoid design results in a very non linearforce profile, and in all changes we are looking to increase the overallforce while improving the low points in the achievable force.

2.1.1 Disk Thickness

Several modeling runs were conducted to study the effect of increasingthe thickness of the coil disks on the peak coil force. It is thoughtthat the disks are in saturation at the inner diameter. Thereforeincreasing the thickness of the disk reduces the saturated diameter ofthe disk, concentrating the coil flux closer to the centre. Thisincreases the available force when the slug is away from the disk buthas little effect as the slug approaches the disk, resulting in littlechange to the low points in the force profile.

For other embodiments, additional work was done looking at tapered disksand other methods of thickening the disk without compromising coilvolume. From this it was seen that the slug force is greatly reducedonce the front face of the slug enters the disk. In one embodiment, a0.3 mm disk offers a good compromise between force and available coilvolume without introducing flat (near zero force) points in a singlecoil energization curve.

2.1.2 Slug Dimensions

Several modeling runs were conducted to study the effect of varying thelength and the inner and outer diameter of the slug on the peak coilforce. In one embodiment, it was found that increasing the slug lengthwas beneficial, so this was set at 4.87 mm. There was also a significantand increasing relationship between outer diameter and peak force—it wasdecided to settle on a slug OD of 3.6 mm in one embodiment. Over therange modeled, the effect of varying inner diameter was negligible,although slug mass was decreased.

The above table shows the effects of increasing the slug dimensions. Thelatter results from ID of 2-3 mm are extrapolated from the results andshow the most promising increase in force available. This force is shownin terms of the Acceleration factor, i.e. the ability of the solenoid toaccelerate the Total Carriage Mass.

From these results we estimate that some controlling factors are theSlug End Area, relating to the area available for the flux lines to actupon and the acceleration factor. Assuming this is correct, in oneembodiment, the desired dimensions for increased force are an OD of 3.6mm with an ID of between 2.6 and 2.8 mm to match to the existing endarea at an OD of 2.4 mm

2.2 Split Slug

In one embodiment, the concept behind the split slug was to even out theforce profile over the whole slug throw by firing two coilssimultaneously, whilst ensuring that when one slug is in an active forceregion, the other is producing no force and vice versa. This route wasparticularly interesting as a way of linearising the force profile.

2.2.1 Split Slug—Testing

In order to test the theoretical force curves, two pairs of metal slugswere made. One set was 2.53 mm long and the other set 2.33 mm. Thesesets were slid onto the end of metal wire with a spacer between thepairs to set the coil pitch at 3.28 mm. This spacer dimension was basedon the simulation data suggesting an optimum gap of 1.41×coil pitch.

In one embodiment, a static test was performed—the force applied to theslug assembly by a single active coil at several fixed positions throughthe coil was measured. The end of the slug assembly was attached to a600 g load cell, and the coil was attached to a track that allowed theslug to be accurately positioned within the solenoid. A 15.6 A constantcurrent supply was applied to the coil for a duration that allowed theforce applied to load cell to stabilize (35 ms).

In one embodiment, starting with the back edge of the slug flat with theback edge of the solenoid “zero position”, the slug was moved in 0.2 mmincrements through the solenoid; this allowed a force profile for theslug and solenoid to be recorded. Profiles were recorded for the 2.53 mmpair of slugs, 2.33 mm pair of slugs, and individual slugs at 2.53 mmand 2.33 mm.

In one embodiment, the static test force profiles for the split slugscan be compared to the results from a previous static test done on afull-length single slug as can be seen in FIG. 28 which illustrates asplit slug force profile. A full length 4.87 mm slug generated 1.5N. Thepeak force for a 2.33 mm slug was 0.92N. The peak force for a 2.53 mmslug was 0.96N. The force on a split slug completely changed directionin 0.8 mm from peak to trough. At the overlap of coil influence amaximum of less than 0.1N could be applied to the slug in eitherdirection.

In some embodiments, by going to a split slug design, the drop in theoverall peak force available was significant. The peaks and troughs inforce are still large enough to make it difficult to assume an effectivelinear control strategy. The large drop in force is likely due to platesaturation. The plates closest to the active coil saturate when turnedon and the magnetic field extends to include the next set of plates, thesmaller slugs are too small to make effective use of the force providedfrom these more distant plates.

2.3 Electrical Improvements

In one embodiment, the main aspect of the electrical system is the powersupply and the FET drive. This system takes up considerable space aslarge capacitors are used to supply sufficient energy to the solenoid.

2.3.1 High Voltage Drive

Referring now to FIG. 29, in one embodiment, the current power supply isbased around a 15.5V boost converter using 20V rated FETs and 16V ratedelectrolytic capacitors. By increasing the voltage which the boostconverter supplies, the energy stored in the capacitors is significantlyimproved in accordance with the equation: Energy=½CV². A higher voltagesystem would use different capacitors and transistors, but thecapacitance used to achieve equivalent energy storage would be greatlyreduced and consequently the size of the capacitors.

Approach

In one embodiment, the next common voltage range of capacitors above 16Vis 35V and therefore it was decided to test a 30V system using anequivalent energy capacity to 13600 μF at 15.5V which is approx. 3300 μFat 30V. In addition the FETs tested were dual FET packages rated55V—Part No. IRF7341

In one embodiment, a test were devised to give a comparison of availableforce between the 15.5V and 30V systems. Static tests could not be usedto obtain a force profile for the higher voltage system, as a steadysupply that could provide the desired energy to the system could not beacquired. A dynamic test was seen as the best alternative and mostaccurate measure of performance for a 30V system.

In one embodiment, the coil was placed vertically so that the slug couldbe fired upwards to reduce the effects of friction in the system. Theslug assembly's weight was adjusted so that it was exactly 1 g, thisenabled the slug to be fired at a slower speeds which reduced encodernoise. A logic analyser running at 100 Mhz was attached to the output ofthe optical encoder in order to log the time at which encoder edgeinputs occurred. The slug was moved so that its back edge was flat withthe rear of the solenoid “zero position” (see FIG. 30).

First—the central coil was pulsed at 100 μs to 1500 μS at 100 μsintervals to check that the acceleration profile was independent ofpulse length.

Second—the starting position for the slug was raised through the coil at0.5 mm intervals to 2.5 mm and the central coil was fired for 1200 μs ateach of these positions.

Finally—in one embodiment, the extra weight on the slug assembly wasremoved (making the weight 0.28 g), this was in order to get a speedcomparison to previous tests performed at 15.5V. The slug was moved sothat its back edge was flat with the rear of the solenoid and thecentral coil was fired for 1200 μs.

During all of the tests at 30V, the current that could be drawn tocharge the capacitors was limited to 0.1 A (0.2 A was allowed for allprevious experiments at 15.5V). For a given starting point all pulsesaccelerated the slug along the same acceleration profile. FIG. 31 showsthe speed traces for different pulse lengths in μSeconds.

In one embodiment, by incrementing the start position of the slugtowards the active coil, the acceleration of the slug appears toincrease. The noise in the system means accurate measurement of thediscrepancies between the acceleration is virtually impossible. However,it was possible to calculate the average force over a broad section ofthe force profile by using the maximum speed achieved and the associatedtime to obtain an average acceleration value. The mass was then dividedin to obtain the force. The noisy position data was not significant overlarge displacements and therefore an average force within thosedisplacements could be calculated using the data shown in FIG. 31.

In one embodiment, by removing the extra weight from the slug and firingit from the zero position with the middle coil the slug reached amaximum speed of 15.5 m/s. The energy in the 3300 μF capacitor with alimited 0.1 A supply was sufficient to accelerate the slug assembly to15.5 m/s and then decelerate the slug to a complete stop without anydeterioration in the acceleration profile. The lower voltage systemshowed some deterioration in acceleration during the braking section ofan equivalent test.

The acceleration profile is independent of the pulse length. The forceon the slug has been increased significantly with no detrimental effectsobserved. This has been done with the use of smaller capacitors ashighlighted by the lower mass experiments. The average force produced bythe 30V system was 6.6N compared to an average force of 3.7N for the15.5V system. The clear advantages of this approach are:

Smaller Capacitors

-   -   Higher forces, giving faster acceleration/deceleration, higher        speeds and increased ability to pull out, push in        static/standing forces    -   Increased magnetic field influence (potentially fewer coils        used)

2.3.2 Recommended Next Steps—Electronics Optimisation

-   -   Change the 15.5V PSU rail to a 30V rail and change the capacitor        size to 3300 mf.    -   A possible further avenue of exploration is to measure PSU        energy use during the complete firing cycle and use these        results to set the absolute minimum size of the capacitor.    -   Redesign of the boost converter using a transformer to optimise        the efficiency of the converter at this higher voltage.

A new rig is currently being designed in order to obtain the higherpositional resolution needed to gain an accurate force profile.

3 Control System Development

3.1 Objective

The launcher system technical objectives include:

-   -   accelerating to a speed of at least 4 m/s.    -   achieving a positional accuracy on stopping of +/−0.05 mm at any        set depth between 0.5 and 3.5 mm    -   retracting from the skin under control at slow speed

The objectives of this part of the work were to create a model to testcontrol algorithms for the system and to create and test the models overa wide range of conditions.

3.2 Approach

3.2.1 Modelling Environment

One embodiment of the launcher system was modelled in Matlab/Simulink.Matlab is a numerical modelling environment able to manipulate andcompute mathematical models based on matrices. It is both command-lineand script driven. Simulink is an extension to Matlab. It is a graphicalenvironment which allows dynamic system modelling using the notation andconventions of control system block diagram models. Models are defined,initialised and then a simulation of their dynamic behaviour is run overa specified time sequence. Using Matlab scripts, multiple model runswere executed enabling fast analysis of model sensitivity to variables.

3.2.2 Model Composition

The Simulink model created is in two parts:

-   -   the controller, which runs the control system software. This        handles all phases of the launch and retract cycle    -   the test shell, which is a model of selected physical features        of the launcher and the electronic input/output system,        essential for testing the controller.

Referring now to FIG. 33, one embodiment of a launcher system model isshown. The approach was modular and iterative—the different systemfunctions of sampling, controlling speed, timing the coil current weresplit so that each could be improved in isolation. The components of themodel are shown in FIG. 7. During the development of the model, somefurther decisions on implementation were taken—chiefly on the PWM/Coildrive system.

The controller has two parts—the state controller and the dynamicscontroller. The state controller is designed to execute the whole launchcycle—acceleration, braking, then slow and fast retraction. The dynamicscontroller deals with adjustments to the coils to achieve control of thecarriage.

The test shell and the controller were both initialised from a Matlabscript which sets up global constants for the current simulation run.During the run, simulation data is output to Matlab where it can bestored and later analysed. The main focus of work during development wason achieving a tight positional accuracy on insertion.

3.2.3 Realism

In operation, the launcher electronic system has many interactions butthe system elements with the biggest impact on the control algorithmare:

-   -   the encoder    -   the technique used to drive the coils    -   the coils themselves.

The some characteristics of the launcher system which were used in themodel are tabulated here:

Skin Skin offset from 4 mm (fixed)¹ rest position Skin force gain 114N/m gives 0.4N @3.5 mm Noise s.d. 3.5% Depth setting 0-3.5 mm in 0.1 mmsteps Encoder Number of channels: 2 Positional resolution: 42.32 μmStandard deviation +/−1 μm of positional measurement: Carriage Mass 2.98g Coil Coil force gain 3N peak Coil offset from 3.5 mm zero positionCoil pitch 2.33 mm PWM PWM period 50 μs resolution 8 bit throttlesetting 50%

3.2.4 Implementability

In order to be fit to implement in a low-end microcontroller, thecontrol algorithm must be constructed from a limited set of mathematicaloperations and run at a speed, which will fit within its computationalcapability. In outline, the mathematical functions that will be usedare:

-   -   16-bit fixed point add/subtract    -   16-bit fixed point multiply/divide    -   Look up table.

During this phase of testing, full 32-bit floating-point arithmetic wasused.

3.2.5 Force Control—Pulse Width Modulation and Coil Firing

To achieve control over the level of coil force developed, the modelcontains a PWM module. This pulses current to the coils in time slots of50 ms. Within this period, the time resolution was 8 bits, giving 256selectable firing durations. Averaged over the PWM period, this givesdirect control of the average force.

Referring now to FIG. 34, a 5 Coils Force Profile is shown.

A simple rule was needed to decide which coil to fire during the cycle.Static force tests on the solenoids provided a force—distance profile(see FIG. 34). The controller was programmed to use the following simpleswitching rule:

In this embodiment, at all positions, select the coil that will generatethe greatest force.

This rule was encoded in 2 tables of 4-elements containing theswitchover points for the 5 coils for insertion and retraction. Becauseof the modular approach, the coil was treated as an instantly respondingactuator. This means that other combinations of coil switching e.g. 2coils at once can be employed within this module without affecting thearchitecture of the system.

3.3 Control Techniques Studied

The physical system (plant) under control is a moving mass system withalmost instantaneous direct control of the applied force. The only plantinformation is the position of the carriage. Two techniques were studiedto achieve positional control.

3.3.1 Acceleration-Based

In one embodiment, acceleration was measured by differentiating theposition signal twice, and averaging this signal over the PWM period.This smoothed value was used as an input to a simple proportionalcontroller, employing no integral or derivative action—see FIG. 35. Theoutput was fed to the PWM module as a time demand—which is translated toa force as described above. The results of this processing werefavourable.

As seen in FIG. 35, a portion of the control algorithm—Accelerationcontrol, is shown.

In this algorithm, the throttle is a logic signal, and the PWM demand isevaluated when triggered every PWM period (50 ms). The PWM demand is asmoothed version of the acceleration error as the sum takes inputs fromboth the current and previous PWM periods. There are three modelparameters—the constant PWM value and the two gain Figures.

The rationale was to create a servo system which would respond quicklyby adjusting the coil force in response to any given accelerationdemand. If this were possible, velocity and position could be controlledaccurately as a result. The acceleration demands are set according to astate controller which runs the launch and retract cycle and is commonto all the models discussed here.

A side effect of measuring the acceleration is a real-time measurementof the coil force during the previous PWM period. The accelerationcontroller's reason for being and its main error input is the variationin coil force caused by the solenoid.

In one embodiment, a forward-looking condition was then used to initiatebraking. The results of testing this algorithm can be seen in FIG. 36and further discussed in FIG. 44. A sign of the correct operation ofthis algorithm is the variation in PWM duty cycle in sympathy tovariation in the coil force, which can be seen. One of the initialfindings about this controller was that it is sensitive to gain valuesthat are coil-dependent. It also failed to use the maximum force regionsof the coils to full advantage, because it was targeting an accelerationvalue which was achievable even in a low coil force region. This wasquite unsatisfactory as a hard braking method.

Following initial testing of this algorithm it was decided to focus onthe energy control algorithm. The acceleration control algorithm was nottested with later model enhancements.

3.3.2 Energy Based

In outline, the 2nd technique of controlling to achieve positionalaccuracy was based on equating the energy available to stop the carriagein the remaining distance with the kinetic energy, which it has at theskin entry point.

The approach was to send the carriage on a braking profile that uses afixed fraction (the energy set point) of the total work available fromthe coils. In practice, this is achieved by setting the PWM value at aconstant fraction of 100% duty. Because the coil force varies withcarriage position, the effect of this on the carriage is to decelerateit on an uneven speed profile. The speed profile can be calculated froma coil force map, which is obtained experimentally, is stored, and formspart of the control algorithm.

Three important quantities are now introduced. These are shown on FIG.37:

-   -   The energy/speed set profile. For a given energy set point, it        is known what the coil force, and therefore the work done by the        coil, will be, throughout braking. The work done on the carriage        by the skin is also known. By adding these together, the total        work done on the carriage is calculated. Therefore, the        idealized profile of carriage kinetic energy against distance        can be calculated for the braking phase. This is used as the set        point profile for control. Assuming there are no errors in the        prediction of force on the carriage, this is the profile the        carriage will follow when braked at the energy set-point with no        intervention from the controller.    -   The total work available to brake the carriage from the skin+the        coils. This is all the work that can be done on the carriage as        it travels to the desired skin depth. It is also the profile        which the carriage would follow under the action of 100% coil        braking and skin force. This defines the control envelope—if the        carriage kinetic energy departs outside this curve, it is        certain to overshoot the stopping point.    -   The difference between the energy set-point and the total work        available is the energy margin. This spare work is used to        correct for errors between the actual speed and the set speed.

In principle, to obtain a high level of braking, a small level of energymargin is used. To compensate for a large level of errors, a largerenergy margin is used. The trade-off between the two can be reduced byimproving the performance of the in-built control system. A diagram ofthe energy control algorithm is shown in FIG. 38.

Referring now to FIG. 38, another portion of the controlalgorithm—energy control, will now be described. In this embodiment,this algorithm is continuously evaluated. A lookup table is used to readthe current Figure for “braking work”. The “skin work” is pre-calculatedby a formula based on skin depth and is also stored in a lookup table.The energy set profile is calculated from the sum of skin work andbraking work (scaled). The error (energy error) produced by subtractingthis from the carriage kinetic energy is then scaled by a gain andmodifies the fixed PWM value.

The main error source which the controller acts on is the error betweenthe predicted force—distance relationship of the skin and its actualvalue, together with the associated variation (skin noise). This istherefore one of the main testing usements.

Implementation—Data Storage

In order to use the concept of a dynamic energy set profile as an inputto the controller, the carriage force profile needs to be stored. Thisis more sophisticated and data intensive than acceleration control. Evenso, 0.1 mm resolution can be achieved to 4.0 mm depth with only 40stored values.

Following initial testing, the performance of the energy-based controlstrategy was promising. In some embodiments, the positional error onstopping was between—0.5 mm and −0.15 mm.

After some testing of different methods for calculating the energy setprofile, it was decided to use the following formula to calculate it:

Take the estimated work available from the skin from entry to stoppingpoint

Add in the work available from coil braking, scaled for the energy setpoint

Sensitivity Study

The control approach described above is data-intensive. There areseveral parameters, which affect the performance of the model to varyingdegrees. An illustration of the variables within each module and theextent to which they are under control is shown in FIG. 39. During thecourse of this study, it was desired to test the effect of variation inthe important factors below to ascertain the level to which they affectsystem performance. Fortunately, the models can be run repeatedly toinvestigate these variables over a range of values. During thesensitivity testing, roughly 100 simulation runs with differentparameters have been completed.

Referring now to FIG. 39, the nature of the module variables will now bedescribed. The effect of each of the parameters highlighted in boldabove on stopping accuracy has been checked. It was decided that thelevel of launcher friction was so low as to be insignificant incomparison to the other active forces (coil and skin force) and thattherefore this was not essential to the model.

Encoder Noise

In one embodiment, positional noise from the encoder affects velocityand acceleration measurements. The effect was characterisedexperimentally. From experimental data, the standard deviation of thisnoise was found to be +/−1 mm. The noise component of this signal wasadded into the model as an error signal. The effect on the velocitymeasurement can be seen in FIG. 1—a noise signal is created. Throughoutmodelling, a value of 1 mm was selected. The limit on encoder noisebeyond which positional control was significantly degraded was 2 mm. Amore complete graph of this effect is shown in FIG. 40.

Coil Force Measurement

In one embodiment, the controller braking profile is based onmeasurements of the coil force conducted in a static force test. Theeffect of variations in these forces was studied and the result is shownin FIG. 40. For the tests shown in this Figure, the predicted coil peakforce was 4N. The actual coil force was varied from 2 to 6N. As can beseen, the effect of underestimating coil force is much less criticalthan that of overestimating it. The stopping accuracy was generallywithin 0.1 mm of the desired stopping point, except at low levels ofactual coil force. In that case, overshooting was more serious, at up to0.3 mm at 3 mm set depth.

Skin Entry Speed

In one embodiment, the skin entry speed was targeted so that duringbraking, the carriage kinetic energy would converge with and run downthe pre-programmed profile. Because of the fact that increased skinpenetration depth brings more energy available from the coils to stop,this naturally means that the deeper the stopping point, the faster theentry speed.

This way of targeting skin entry speed is not optimised for flight time,as the carriage could be driven faster in the early part of its flight,then braked before entering the skin. This refinement is particularlyrelevant for shallower depths but was not seen as useful to the setdepth accuracy problem. Either side of its velocity set point, thebraking controller has a “capture window” within which it can bring andkeep the velocity under control during braking. Outside of this windowthe carriage either ends up overshooting, because the energy margin hasbeen used up, or the carriage has insufficient momentum to enable it toreach its desired position and it stops short.

A refinement that could be tested to deal with either of theseeventualities was asymmetric gain.

Coil Usage

During the full insertion and retraction cycle, coil 0 alone is used forbraking and acceleration. Because this aspect of the model is fullyparametric, the force profile for predicted coils and actual coils canbe quickly modified and retested when other coil layouts are tried.

Sensitivity to Errors in Skin Force Prediction

In one embodiment, the algorithm improves positional stoppingperformance by including a prediction of skin force and hence energy.This estimate was obtained from experimental data. By including thisprediction, it introduces sensitivity to that data. Testing wasconducted to explore the effects of errors of factors x2 and x½ in theaverage skin force for comparison with nominal data. The results areshown in FIGS. 43 and 44 below show these three skin force gainscenarios.

The graph in FIG. 42 is encouraging—it shows the overall performance ofthe algorithm over a range of set depths and skin force gains.

At deeper set depths, the sensitivity of the positional accuracy toerrors in skin force is greater than at lower depths. This is to beexpected intuitively, as the work done by the skin increases as aquadratic function of distance.

At lower set depths, the entry speed was simply too low to enable thealgorithm to work effectively. This needs more complete testing andprobably a different approach for shallow entry. It should be borne inmind that in this testing, the energy control concept was onlyimplemented within the skin and not in free space.

One of the best ways counteract errors in skin force prediction is tomake the total possible error small in relation to the coil force, whichcan be controlled. This is done by increasing the coil force. The effectof this can be seen in the earlier FIG. 41 and also in FIG. 43. Thethree traces show simulations conducted at the same coil force andstopping error was greater when skin force was underestimated (redtrace).

-   -   In general, the control algorithm involves using a        pre-programmed speed profile at a fixed coil throttle setting        and using what coil force is left to cancel out errors arising        from skin and other forces.    -   Studies of sensitivity to errors in predicted skin force,        encoder noise and to variation in coil force have been conducted        and the effects recorded.    -   Using a higher force in relation to skin force enables more        precise positioning to be achieved.

Using a peak coil force of 3N, insertion positioning to within +/−0.1 mmcan be achieved over a range of set depths from 1 to 3.5 mm and over arange of skin—force curves. At lower coil forces, positioning accuracyis degraded.

Control System Development

-   -   Control algorithm—Test the idea of using an asymmetric gain on        the energy error signal during braking. Include a model of the        launcher friction. Change the method of calculating the energy        set profile for shallow skin entry.    -   Implementation—Construct a prototype system using MatLab RTW to        produce real time code to run on MatLab XPC real time PC system.        This will allow further testing and development of the control        algorithm on the real hardware and skin.    -   Implementation—Model the system using only 16-bit arithmetic and        change the energy-based algorithm to a velocity-based one to        maintain signal precision.    -   Implementation—Modify the algorithm to operate at the (much        slower) PWM frequency, rather than in near real-time.    -   Testing—Test the revised algorithms using a similar test suite        as described here.    -   Experimental/mechanical data—Update the coil force graphs and        dimensional parameters for the latest mechanical layout

4 Position Sensors—LVDT

In one embodiment, a linear variable differential transformer is analternative to the optical encoder as a means of position and speedsensing. In a successful realisation, the chief advantages over theoptical encoder are:

-   -   a higher linear resolution    -   a smaller package size and a shape which is easier to integrate    -   The ability to provide position updates to the microcontroller        on request, rather than having an interrupt-driven system, which        aids software design.

Lower Cost

The simple basic design of the LVDT is versatile and offers a wide scopefor customisation. LVDTs also offer fast dynamic response, they can makemeasurements at up to 1/10 of the driving frequency on the primarywinding. For this application, that translates into an ability to sensemovement at >50 m/s. Although widely used in industrial equipment, theyare rarely found in low cost consumer items. The objective for thisstudy is to prototype a design and to find an optimal solution for thelauncher.

4.1 Design Issues

Operating frequency Needs to provide positional updates at a rate closeto that of the current sensor (4-5 ms). May be possible to go to 10 ms.Assuming an ADC system is used where the ADC can sample successivepeaks, then the driving sine wave source frequency is in the range 100kHz to 250 kHz. For this application it should be able to sense movementat >50 m/s. The maximum frequency of the coil drive is limited by aircoupling

Resolution To match the encoder resolution uses 1024 positional steps—10bits

Moving weight Must not adversely affect the performance of thesolenoid—carriage system.

Packaging Length<30 mm, diameter<8 mm

System BOM cost, including electronics <$3.00

Throw distance 8 mm

Table 2: Outline LVDT specification

The LVDT electronics is comprised of the following elements:

-   -   Drive circuit. For low component count and design simplicity, it        makes sense to control the LVDT drive directly from the        microcontroller.    -   Sense/sample circuit. Must provide gain and offset zeroing and        also the ability to hold the signal for the ADC.    -   ADC. Must provide sufficient conversion speed to satisfy the        frequency usement.

4.2 Coil Parameters

4.2.1 Coil Disposition

The layout of the coils in commercial LVDT products is such that theymay be used in a single ended mode, ie a moving soft metal slug entersfrom one end only. A simpler design could be a centre primary with twosecondary windings. In this case the slug length is the primary length+asingle secondary length.

By careful design of the numbers of turns and dimensions of the primaryand secondary some gain can be achieved within the LVDT to improve thesignal to noise ratio of the secondary signals.

4.2.2 Single Coil

LVDTs traditionally have two coils, each of which produces an outputwhich is linearly proportional to the position of the slug. Whensubtracted, the two voltages cancel at a zero position. This removes theeffect of air coupling. If the sensing/sampling circuit can be designedsuch that the air offset is zeroed then a single secondary coil can beused. This would produce significant packaging benefits.

4.2.3 Recommended Next Steps—LVDT

Purchase a commercial LVDT and develop suitable drive circuitry forinterface to a microcontroller system.

Referring now to FIG. 44, a predictive braking algorithm is shown. Bymodeling the penetrating member driver and the tissue to be penetrated,a “road map” of short is provided to determine when the braking shouldbe applied to achieve a desired depth. Feedforward systems are describedherein and are used in combination with a lancing device such as thatdescribed in commonly assigned U.S. patent application Ser. No.10/127,395 (now U.S. Pat. No. 7,025,774) and 38187-2606. Feedback isused in combination with feed forward. In this embodiment, feedforwardmay be used for braking of the penetrating member or more precisely, theslug driving the penetrating member. The feed forward algorithm may bestored in a processor used to control the penetrating member driver.FIG. 44 shows in detail how the planned velocity is used to determinehow to reach a desired depth. In one embodiment, the entire inbound pathis traveled in under 10 ms, which is faster than most humans can see.Hence the need for feedforward to provide a planned velocity so that theaccurate depth can be reached without lag and/or instability that may beassociated with a feedback only system.

As each device is manufactured, each driver may be modeled duringmanufacturing to adjust the model for each driver. In other embodiments,a standard model may be used.

While the invention has been described and illustrated with reference tocertain particular embodiments thereof, those skilled in the art willappreciate that various adaptations, changes, modifications,substitutions, deletions, or additions of procedures and protocols maybe made without departing from the spirit and scope of the invention.For example, with any of the above embodiments, the location of thepenetrating member drive device may be varied, relative to thepenetrating members or the cartridge. With any of the above embodiments,the penetrating member tips may be uncovered during actuation (i.e.penetrating members do not pierce the penetrating member enclosure orprotective foil during launch). With any of the above embodiments, thepenetrating members may be a bare penetrating member during launch. Withany of the above embodiments, the penetrating members may be barepenetrating members prior to launch as this may allow for significantlytighter densities of penetrating members. In some embodiments, thepenetrating members may be bent, curved, textured, shaped, or otherwisetreated at a proximal end or area to facilitate handling by an actuator.The penetrating member may be configured to have a notch or groove tofacilitate coupling to a gripper. The notch or groove may be formedalong an elongate portion of the penetrating member. With any of theabove embodiments, the cavity may be on the bottom or the top of thecartridge, with the gripper on the other side. In some embodiments,analyte detecting members may be printed on the top, bottom, or side ofthe cavities. The front end of the cartridge maybe in contact with auser during lancing. The same driver may be used for advancing andretraction of the penetrating member. The penetrating member may have adiameters and length suitable for obtaining the blood volumes describedherein. The penetrating member driver may also be in substantially thesame plane as the cartridge. The driver may use a through hole or otheropening to engage a proximal end of a penetrating member to actuate thepenetrating member along a path into and out of the tissue.

In one embodiment of the present invention, an LVDT position sensormodule will now be described. As a nonlimiting example, the LVDT,incorporating the bobbin 710, primary coil, core and secondary coils.FIGS. 45 and 46 show one embodiment of a bobbin 710 according to thepresent invention. The bobbin 710 may include a coil separator 712.Secondary coils may be wound over regions 714 and 716. The hub portion718 may be removed after manufacturing to further decrease the size ofthe bobbin 710. The diameter of the bobbin 710 may be varied. The lengthis determined by the through distance and a slight variance for magneticeffects. In one embodiment, the coils are 0.6 mm wire. The layersdetermines the number of coils. The fewer turns used, the less field youget. The present embodiment may have four layers for the secondary andtwo for the primary coil. It should be understood that othercombinations of layers such as two and one may also be used. It is seenthat a physical wall 712 is used to separate the coils (not shown). Thisprovides for simplified manufacturing. The coils may be wound in auniform manner, in one embodiment. A processor may be used tointerpolate the nonlinear output from the coils. Each processor may becalibrated to the output to linearize it. In further embodiments, a wall712 may be removable after the coils are wound. In still furtherembodiments, a clamp may be placed on the bobbin during winding and maybe removed after the coils are wound.

The entire system may also include coil drive electronics, signalconditioning and microcontroller hardware, and firmware to control themicrocontroller modules and process the incoming signal.

One reason for considering the LVDT as a position sensor is because ofits advantages over an optical encoder. These break down into advantagesfor the product (the potential for lower cost manufacture and improvedpackaging), as well as functional advantages for the control system:(high speed, high accuracy on-demand position measurement).

Desired Features

To replace a linear encoder as a position and speed sensor, the LVDTmodule desire to have at least one of the following: Size—as small aspossible; stability—the encoder module is stable with temperature, sothe LVDT should be too; range/resolution—20 m across the measurementrange of 8 mm; response time/update frequency—5 s/200 kHz; and/or movingmass—as low as possible, to limit the effect on carriage ballistics.

Referring now to FIG. 46, a generic system schematic showing the modulesand their relationships is shown. In one embodiment, for its operation,the module relies in part on the timing relationship between the signalwhich is used to drive the LVDT primary coil, sourced in this embodimentfrom a PWM module, and the sampling time of a 10-bit ADC. As anonlimiting example, these may both be integral blocks on board a 16-bitmicrocontroller. These blocks operate in synchronism, which reduces theneed for external componentry. The phase delay is set by internalmicrocontroller settings and by parameters of the external circuit. ADCsampling time is synchronized with the input signal in the presentembodiment.

FIG. 48 shows the timing of the signals of interest. FIG. 49 shows oneembodiment of the drive electronics which implement the coil drive andsignal conditioning. During initial testing, a working frequency for theprimary drive circuit was chosen in one embodiment which enables the ADCto make one sample for every cycle of the LVDT drive signal. By theadjustment of the phase delay, the ADC can be made to sample at the peakof the secondary coil cycle, thereby making the best use of theavailable positional resolution. As seen in FIG. 48, the system may usea square wave input 750. A resonant circuit may be used to convert thissquare wave into a sinusoidal waveform to drive the primary coil. Inthis embodiment, sampling by the ADC is related to the square wave input750. It should be understood that a sine wave generator may also be usedin some embodiments. A certain delay may be used so that the samplingoccurs a the optimal point 752 (as seen in FIG. 48).

By synchronizing the timing of the ADC samples to the drive signal andby using the internal sample and hold circuit, the design of thisembodiment avoids the need to include external rectification or holdcircuitry.

LVDT Primary Coil Drive

The LVDT desires a sine wave to drive the primary coil: this is achievedby exciting a parallel resonant LC circuit with a square wave input(TIOCA1—Vdrive signal). This is then amplified (U1C) to create a lowerimpedance source for the primary coil. The LC circuit is adjusted toresonate at the module operating frequency and R3 is used to limit theoutput amplitude. R4 compensates for the primary coil DC impedance toprevent output clipping on U1C.

Coupling and Secondary Coil Signal Conditioning

The voltage ratio of the LVDT is a function of the turns ratio and thegeometry of the coils. This is chosen, alongside all the gains in thesignal path, to preserve SNR. The secondary coil voltage is fed througha standard high gain differential amplifier (U1D) before being fed intothe ADC. The choice of resistor values for U1D is driven by the need toobtain maximum gain without loading the LVDT secondary coil or theop-amp excessively. The entire LVDT drive circuit is referenced to astabilised mid-rail voltage to use the op-amps most effectively.

ADC Conversion and Signal Processing

The timing of the ADC sampling and conversion process is shown at thebottom of FIG. 4. The ADC is triggered by the TPU, which also suppliesthe PWM signal. It samples near the peak of the negative goinghaft-cycle. The ADC voltage reference pin, Vref, is set-up so that theADC gives its full 10-bit resolution over the anticipated voltage swingof the amplified LVDT secondary signal at the sampling time. With theLVDT optimally set up, this the whole PSU rail voltage. The output fromthe ADC as the LVDT core was moved over its travel can be seen in FIG.50. A look-up table of 13 calibration values was used to encode the ADCcounts over a range from 7.50 to 14.00 mm. The sampling of the ADC maybe increased from 10 ms to 7 ms (40 kHz) depending on themicrocontroller used.

Module Components

Drive Electronics—Op-Amp Circuit

In one embodiment, the rail-to-rail op-amp chosen for the prototypecircuit was the National LM824. From the table below, it was chosenbecause it is a low cost device, it has a 3.3V capability, a respectablegin-bandwidth product of 5 MHz acceptable input offset voltage andoutput drive capability, whilst offering 4 channels of gain.

In the three instances in which it is used, there are differingrequirements. In each one current drive capability and gain bandwidthproduct are the most important

Mid-Rail Supply—U1B, Coil Drive—U1C

In both these instances, the closed loop gain is 1, so the greatestrequirement is for output drive capability. When testing the LVDT #0,the 75 R resistor was necessary to prevent output clipping. With LVDTs#1-#4, this was reduced to 27 R.

Secondary Gain—U1D

The op-amp was set-up to give a closed-loop gain of 1 at 100 kHz whichis well within its gain—bandwidth capability. This op-amp will cope with200 kHz testing, and it may be possible to specify an op-amp with alower GBW product, and reduce cost further.

Microcontroller Hardware—ADC/TPU

The LVDT circuit was prototyped on a Hitachi H8S2318, running at 20 MHz.The operating frequency of the circuit was 100 kHz. One of the limitingfactors on this is the ADC conversion time, which was measured at 5.8 s.This conversion rate is slower than the Adc on the proposed H8S3694microcontroller, which is specified at 3.5 s.

Module Performance

In one embodiment, two designs of LVDT were tested. LVDT #0 was a simpledesign with three similar coils adjacent to each other. LVDTs #1 to #4were made to the design shown in FIGS. 45 and 46, with a primary coilrunning the whole length of the coil and 2 secondary coils overwound oneach half-section.

Repeatability

Between Calibrations

In this embodiment, the calibration curve of LVDT #0 was measured onthree occasions. Across the whole calibration range of 27 mm, themaximum deviation from the mean reading was +/−3 counts (0.79%) and thestandard deviation of 1.12 counts (0.29%).

Between Coils

Three identical examples of the same design, LVDTs #1, #2, #3 wereconstructed and calibrated. The results of the calibration curves areshown in FIGS. 8 and 9 below. Across the whole calibration range, theoverall standard deviation between readings of the three coils was 5.82counts (1.10% of range). This equates to a maximum positional error of0.30 mm when the reading is calibrated in mm.

Since the mechanical system provides a known starting reference, allmeasurements are relative to the zero point. This error should notaffect the penetrating member positional accuracy.

Temperature Stability

The sensitivity of the LVDT and its drive electronics to temperaturevariation was measured across the usable temperature range, by bothheating and cooling the prototype assembly and performing a calibration.The results are displayed in FIGS. 50 and 51. FIGS. 48 and 49: LVDT #2Combined calibration chart—hot and cold readings, positional errors inacross temperature range across usable position range

In one embodiment, the maximum error in ADC count measured over thetemperature range would equate to an error of 0.9 mm in the worst case.The maximum positional error within the usable range was 0.48 mm. Thislevel of error requires further attention to reduce it because thiserror will be evident in the course of the normal use of the product. Itis thought that this is caused by changes in the resistance of the LVDTcoil; temperature-resistance changes within the op-amps and theancillary resistors, and especially the primary drive circuit.

Resolution

The resolution of the LVDT module depends on two factors:

The ADC resolution

The rate of change of output amplitude of the secondary coil withrespect to the core position: the higher the better.

For this embodiment, the ADC resolution was fixed at 10-bits. Within therange provided by this, the resolution was limited by the maximum signalamplitude which could be achieved from the secondary coil amplifier.Calibration curves for the first prototype LVDT, #0, and for #1-#3 areshown in FIGS. 51 and 52 below. The usable range of the LVDT ishighlighted on each figure. For LVDT 0, FIG. 7 shows that the raw ADCcount changes rapidly with position between 7 and 14 mm offset and thisis the region where the resolution was highest on this LVDT prototype.Over this range, the resolution varied between 0.025 mm and 0.014 mm.FIGS. 52 and 53: Calibration charts—LVDT #0, and LVDTs #1-#3 (combined)

To check the effect of counterwinding, one of the secondary coils waswound in the opposite sense to all the other coils. As expected, theeffect was the same as that of switching coil polarity, with no changein the amplitude/position relationship.

Physical Dimensions

For one embodiment, Some 2D sketches of the LVDT bobbin are shown inFIGS. 54 and 55. The overall length is governed by the throw distanceand the diameter is governed by the minimum achievable wall thicknessesand the number of turns wound. The representative outer dimensions ODfor this iteration were OD 3.65 mm, length 23 mm. This would create apackaged volume of approximately 340 mm3. For the encoder, the volume tobe packaged is approximately 1100 mm3. In a future design iteration, thenumber of turns wound could be reduced by approximately 25% before anydetrimental effects were noticed which would further benefit packaging.

Effect of Core Size

In one embodiment, a calibration was attempted using an 8 mm core, andthe result was that the level of coupling was decreased but the overallrange between secondary peaks was unaffected. This suggests thatreducing the core length will have no beneficial effect in increasingthe usable throw distance. It is estimated that this can be reduced byat least 50% in further trials. In one embodiment, the following

Parameter LVDT module Stability Coil-to-coil repeatability: 0.30 mmTemperature: 0.50 mm over operating temp range and usable calibrationrange Range/Resolution 8 mm/20 μm Response time On-demand. 200 kHz/5 μswith 3694 microcontroller. Tested at 100 kHz/10 μs Moving mass 0.163 gSize 340 mm³

Coils Parameter Value #0 Turns ratio - 1:1:1 (primary/secondary A,secondary B) Primary resistance 1.1 ohm Resolution 20 μm Secondaryresistance 2.1 ohm Repeatability 0.29% Range 7 mm #1-#3 Turns ratio -1:1:1 (primary/secondary A, secondary B) Primary resistance 32 ohmSecondary resistance 34.5/34.5 ohm Repeatability between coils 1.10%Resolution 20 μm Range at this resolution 7 mm

In yet another embodiment, a solenoid-based actuator has been developedto move penetrating members into skin for the purpose of collectingblood for the analysis of blood glucose. To reduce pain and improveblood yield, the speed, acceleration, and position of the actuatingsolenoid is controlled. In this embodiment, control is provided by aprocessor that monitors the actuation cycle and modulates the electricalpower to the solenoid. Commercially available position transducers (suchas Hewlett Packard HEDS9731) are being used to provide actuator positioninformation.

In one embodiment, the present invention consists of a Linear VariableDifferential Position Transducer (LVDT) that has been modified toprovide a low profile design. LVDT's are commonly available such as fromSolartron (704) 868-4661 and consist of adjacent cylindrically woundcoils with a soft iron coupling slug that moves inside the coils. Energyfrom an excitation coil is coupled into two secondary coils inproportion to the slug position within the coils. Available LVDT's arecylindrical so the height and width are equal.

Referring now to FIG. 10, to create a more compact LVDT, in oneembodiment, the excitation and driven coils could be wound as flat coilsand placed next to each other in a plane. The moving slug 100 would thentake the form of a flat plate of soft iron that moves in a planeparallel to the coil plane, and close to it. The resulting transducer102 would be thin relative to its width and would make more efficientuse of space. The price for a more compact design would be efficiency ofcoupling, and possibly accuracy.

One arrangement of coils, as illustrated in FIG. 54, would consist of alarge rectangular driving coil wound in a flat open shape. Inside thedriver coil 104, two smaller rectangular or square coils 106 would bemounted side-by-side. The slug would move along the long axis of thedriving coil. FIGS. 55 and 56 provide views of the coil. Specifically,FIG. 56 shows the slug removed and the coils 104 and 106 exposed.

Another arrangement of coils would be similar, with sensing coils insidea driving coil, but the coils may be traces etched onto a thin PCB orflex circuit. Multiple PCB's and/or flex circuits could be stacked toprovide more coil turns.

An alternate arrangement of the slug would consist of a soft iron plateof sheet metal, formed into a “U” so as to enclose the coils on threesides. This wrap-around slug would provide better coupling between thecoils at the cost of more moving mass.

In this embodiment, the primary coil was supplied with 13 Amp turns. Thesecondary coils have 640 turns each. The emf induced in each secondarycoil was determined at various positions of the c-slug, from fullycovering the 2 coils to fully uncovering them. FIG. 57 below shows thedifferential between the 2 coils emf and their sum also. The values wereobtained at 60 Hz in the primary coil. The sensitivity appears to beabout 3 mV/mm, in the linear section of the sum curve.

FIG. 58 below is similar to the one above but the values were obtainedat 6,000 Hz in the primary coil. The sensitivity appears to haveincreased to 22 mV/mm, in the linear section.

In one embodiment, the linear section of the travel appears to be about3.5 mm. This can be increased to 8 mm by doubling the width of thesecondary coils to 4 mm each. The number of turns of these secondarycoils is determined by the packing factor and the fineness of the wireused. The number of turns and current in the primary coil can be chosenfor the most appropriate match with the available supply to produce thenecessary amp-turns.

In one embodiment, the C-slug was assigned mild steel for material. Thethickness can be reduced significantly since the levels of flux densityin the present cross-section are very low. It is probably sufficient tohave a steel sheet on one side of the coils only to produce the requiredlinear emf curves. The material of the frame can be either magnetic ornon-magnetic, since no effect was seen on the emf values.

In one embodiment, a position transducer for detecting mechanismcomponent position is provided. The transducer functions by winding flatcoils and placing driver and driven coils inside each other; couplingcoils with a moving flat soft iron plate or forming the moving soft ironplate so it encloses the coils on three or more sides. The coils may becreated by etching a PCB or flex circuit. A position transducer isdescribed that works on the LVDT principle and is very compact. Thelow-profile form of the transducer is achieved by using flat, coplanarcoils and a flat coupling slug.

In one embodiment, the shaft 110 may be covered with a magnetic layer.Plating of magnetic material on the carbon fiber rod would reduce themass of the slug. Moving mass reduction will allow for improvedacceleration.

Referring now to FIG. 59, a still further embodiment of a cartridgeaccording to the present invention will be described. FIG. 59 shows oneembodiment of a cartridge 900 which may be removably inserted into anapparatus for driving penetrating members to pierce skin or tissue. Thecartridge 900 has a plurality of penetrating members 902 that may beindividually or otherwise selectively actuated so that the penetratingmembers 902 may extend outward from the cartridge, as indicated by arrow904, to penetrate tissue. In the present embodiment, the cartridge 900may be based on a flat disc with a number of penetrating members suchas, but in no way limited to, (25, 50, 75, 100, . . . ) arrangedradially on the disc or cartridge 800. It should be understood thatalthough the cartridge 900 is shown as a disc or a disc-shaped housing,other shapes or configurations of the cartridge may also work withoutdeparting from the spirit of the present invention of placing aplurality of penetrating members to be engaged, singly or in somecombination, by a penetrating member driver.

Each penetrating member 902 may be contained in a cavity 906 in thecartridge 900 with the penetrating member's sharpened end facingradially outward and may be in the same plane as that of the cartridge.The cavity 906 may be molded, pressed, forged, or otherwise formed inthe cartridge. Although not limited in this manner, the ends of thecavities 906 may be divided into individual fingers (such as one foreach cavity) on the outer periphery of the disc. The particular shape ofeach cavity 906 may be designed to suit the size or shape of thepenetrating member therein or the amount of space desired for placementof the analyte detecting members 808. For example and not limitation,the cavity 906 may have a V-shaped cross-section, a U-shapedcross-section, C-shaped cross-section, a multi-level cross section orthe other cross-sections. The opening 810 through which a penetratingmember 902 may exit to penetrate tissue may also have a variety ofshapes, such as but not limited to, a circular opening, a square orrectangular opening, a U-shaped opening, a narrow opening that onlyallows the penetrating member to pass, an opening with more clearance onthe sides, a slit, a configuration as shown in FIG. 75, or the othershapes.

In this embodiment, after actuation, the penetrating member 902 isreturned into the cartridge and may be held within the cartridge 900 ina manner so that it is not able to be used again. By way of example andnot limitation, a used penetrating member may be returned into thecartridge and held by the launcher in position until the next lancingevent. At the time of the next lancing, the launcher may disengage theused penetrating member with the cartridge 900 turned or indexed to thenext clean penetrating member such that the cavity holding the usedpenetrating member is position so that it is not accessible to the user(i.e. turn away from a penetrating member exit opening). In someembodiments, the tip of a used penetrating member may be driven into aprotective stop that hold the penetrating member in place after use. Thecartridge 900 is replaceable with a new cartridge 900 once all thepenetrating members have been used or at such other time or condition asdeemed desirable by the user.

Referring still to the embodiment in FIG. 59, the cartridge 900 mayprovide sterile environments for penetrating members via seals, foils,covers, polymeric, or similar materials used to seal the cavities andprovide enclosed areas for the penetrating members to rest in. In thepresent embodiment, a foil or seal layer 920 is applied to one surfaceof the cartridge 900. The seal layer 920 may be made of a variety ofmaterials such as a metallic foil or other seal materials and may be ofa tensile strength and other quality that may provide a sealed, sterileenvironment until the seal layer 920 is penetrate by a suitable orpenetrating device providing a preselected or selected amount of forceto open the sealed, sterile environment. Each cavity 906 may beindividually sealed with a layer 920 in a manner such that the openingof one cavity does not interfere with the sterility in an adjacent orother cavity in the cartridge 800. As seen in the embodiment of FIG. 59,the seal layer 920 may be a planar material that is adhered to a topsurface of the cartridge 800.

Depending on the orientation of the cartridge 900 in the penetratingmember driver apparatus, the seal layer 920 may be on the top surface,side surface, bottom surface, or other positioned surface. For ease ofillustration and discussion of the embodiment of FIG. 59, the layer 920is placed on a top surface of the cartridge 800. The cavities 906holding the penetrating members 902 are sealed on by the foil layer 920and thus create the sterile environments for the penetrating members.The foil layer 920 may seal a plurality of cavities 906 or only a selectnumber of cavities as desired.

In a still further feature of FIG. 59, the cartridge 900 may optionallyinclude a plurality of analyte detecting members 908 on a substrate 922which may be attached to a bottom surface of the cartridge 900. Thesubstrate may be made of a material such as, but not limited to, apolymer, a foil, or other material suitable for attaching to a cartridgeand holding the analyte detecting members 908. As seen in FIG. 59, thesubstrate 922 may hold a plurality of analyte detecting members, such asbut not limited to, about 10-50, 50-100, or other combinations ofanalyte detecting members. This facilitates the assembly and integrationof analyte detecting members 908 with cartridge 900. These analytedetecting members 908 may enable an integrated body fluid samplingsystem where the penetrating members 902 create a wound tract in atarget tissue, which expresses body fluid that flows into the cartridgefor analyte detection by at least one of the analyte detecting members908. The substrate 922 may contain any number of analyte detectingmembers 908 suitable for detecting analytes in cartridge having aplurality of cavities 906. In one embodiment, many analyte detectingmembers 908 may be printed onto a single substrate 922 which is thenadhered to the cartridge to facilitate manufacturing and simplifyassembly. The analyte detecting members 908 may be electrochemical innature. The analyte detecting members 908 may further contain enzymes,dyes, or other detectors which react when exposed to the desiredanalyte. Additionally, the analyte detecting members 908 may comprise ofclear optical windows that allow light to pass into the body fluid foranalyte analysis. The number, location, and type of analyte detectingmember 908 may be varied as desired, based in part on the design of thecartridge, number of analytes to be measured, the need for analytedetecting member calibration, and the sensitivity of the analytedetecting members. If the cartridge 900 uses an analyte detecting memberarrangement where the analyte detecting members are on a substrateattached to the bottom of the cartridge, there may be through holes (asshown in FIG. 76), wicking elements, capillary tube or other devices onthe cartridge 900 to allow body fluid to flow from the cartridge to theanalyte detecting members 908 for analysis. In other configurations, theanalyte detecting members 908 may be printed, formed, or otherwiselocated directly in the cavities housing the penetrating members 902 orareas on the cartridge surface that receive blood after lancing.

The use of the seal layer 920 and substrate or analyte detecting memberlayer 822 may facilitate the manufacture of these cartridges 10. Forexample, a single seal layer 920 may be adhered, attached, or otherwisecoupled to the cartridge 900 as indicated by arrows 924 to seal many ofthe cavities 906 at one time. A sheet 922 of analyte detecting membersmay also be adhered, attached, or otherwise coupled to the cartridge 900as indicated by arrows 925 to provide many analyte detecting members onthe cartridge at one time. During manufacturing of one embodiment of thepresent invention, the cartridge 900 may be loaded with penetratingmembers 902, sealed with layer 920 and a temporary layer (not shown) onthe bottom where substrate 922 would later go, to provide a sealedenvironment for the penetrating members. This assembly with thetemporary bottom layer is then taken to be sterilized. Aftersterilization, the assembly is taken to a clean room (or it may alreadybe in a clear room or equivalent environment) where the temporary bottomlayer is removed and the substrate 922 with analyte detecting members iscoupled to the cartridge as shown in FIG. 59. This process allows forthe sterile assembly of the cartridge with the penetrating members 902using processes and/or temperatures that may degrade the accuracy orfunctionality of the analyte detecting members on substrate 922. As anonlimiting example, the entire cartridge 900 may then be placed in afurther sealed container such as a pouch, bag, plastic molded container,etc. . . . to facilitate contact, improve ruggedness, and/or allow foreasier handling.

In some embodiments, more than one seal layer 920 may be used to sealthe cavities 906. As examples of some embodiments, multiple layers maybe placed over each cavity 906, half or some selected portion of thecavities may be sealed with one layer with the other half or selectedportion of the cavities sealed with another sheet or layer, differentshaped cavities may use different seal layer, or the like. The seallayer 920 may have different physical properties, such as those coveringthe penetrating members 902 near the end of the cartridge may have adifferent color such as red to indicate to the user (if visuallyinspectable) that the user is down to say 10, 5, or other number ofpenetrating members before the cartridge should be changed out.

Referring now to FIG. 60, one embodiment of an apparatus 980 using aradial cartridge 900 with a penetrating member driver 982 is shown. Acontoured surface 884 is located near a penetrating member exit port986, allowing for a patient to place their finger in position forlancing. Although not shown, the apparatus 980 may include a humanreadable or other type of visual display to relay status to the user.The display may also show measured analyte levels or other measurementor feedback to the user without the need to plug apparatus 980 or aseparate test strip into a separate analyte reader device. The apparatus980 may include a processor or other logic for actuating the penetratingmember or for measuring the analyte levels. The cartridge 900 may beloaded into the apparatus 980 by opening a top housing of the apparatuswhich may be hinged or removably coupled to a bottom housing. Thecartridge 900 may also drawn into the apparatus 980 using a loadingmechanism similar in spirit to that found on a compact disc player orthe like. In such an embodiment, the apparatus may have a slot (similarto a CD player in an automobile) that allows for the insertion of thecartridge 900 into the apparatus 980 which is then automatically loadedinto position or otherwise seated in the apparatus for operationtherein. The loading mechanism may be mechanically powered orelectrically powered. In some embodiments, the loading mechanism may usea loading tray in addition to the slot. The slot may be placed higher onthe housing so that the cartridge 900 will have enough clearance to beloaded into the device and then dropped down over the penetrating memberdriver 982. The cartridge 900 may have an indicator mark or indexingdevice that allows the cartridge to be properly aligned by the loadingmechanism or an aligning mechanism once the cartridge 900 is placed intothe apparatus 980. The cartridge 900 may rest on a radial platform thatrotates about the penetrating member driver 982, thus providing a methodfor advancing the cartridge to bring unused penetrating members toengagement with the penetrating member driver. The cartridge 800 on itsunderside or other surface, may shaped or contoured such as withnotches, grooves, tractor holes, optical markers, or the like tofacilitate handling and/or indexing of the cartridge. These shapes orsurfaces may also be varied so as to indicate that the cartridge isalmost out of unused penetrating members, that there are only fivepenetrating members left, or some other cartridge status indicator asdesired.

A suitable method and apparatus for loading penetrating members has beendescribed previously in commonly assigned, copending U.S. Pat. No.38187-2589 and U.S. Ser. No. 60/393,707, and are included here byreference for all purposes. Suitable devices for engaging thepenetrating members and for removing protective materials associatedwith the penetrating member cavity are described in commonly assigned,copending U.S. patent applications 60/422,988 and 60/424,429, and areincluded here by reference for all purposes. For example in theembodiment of FIG. 59, the foil or seal layer 920 may cover the cavityby extending across the cavity along a top surface 990 and down alongthe angled surface 892 to provide a sealed, sterile environment for thepenetrating member and sensors therein. A piercing element described inU.S. patent applications 60/424,429 has a piercing element and then ashaped portion behind the element which pushes the foil to the sides ofthe cavity or other position so that the penetrating member 902 may beactuated and body fluid may flow into the cavity.

Referring now to FIG. 61, one embodiment of a device that may use a disc900 is shown. This embodiment of device 1000 include a display 1002 thatshows lancing performance and setting such as penetration depth settingthe like. Various buttons 1004 may also be placed on the housing toadjust settings and/or to activate lancing.

It should be understood that device 1000 may include a processor forimplementing any of the control methodologies set forth herein. Theprocessor may control the penetrating member driver and/or activebraking device such a pads, stops, dampers, dashpots and other mechanismto control penetrating member speed. The characteristic phases ofpenetrating member advancement and retraction can be plotted on a graphof force versus time illustrating the force exerted by the penetratingmember driver on the penetrating member to achieve the desireddisplacement and velocity profile. The characteristic phases are thepenetrating member introduction phase A-C where the penetrating memberis longitudinally advanced into the skin, the penetrating member restphase D where the penetrating member terminates its longitudinalmovement reaching its maximum depth and becoming relatively stationary,and the penetrating member retraction phase E-G where the penetratingmember is longitudinally retracted out of the skin. The duration of thepenetrating member retraction phase E-G is longer than the duration ofthe penetrating member introduction phase A-C, which in turn is longerthan the duration of the penetrating member rest phase D.

The introduction phase further comprises a penetrating member launchphase prior to A when the penetrating member is longitudinally movingthrough air toward the skin, a tissue contact phase at the beginning ofA when the distal end of the penetrating member makes initial contactwith the skin, a tissue deformation phase A when the skin bendsdepending on its elastic properties which are related to hydration andthickness, a tissue lancing phase which comprises when the penetratingmember hits the inflection point on the skin and begins to cut the skinB and the penetrating member continues cutting the skin C. Thepenetrating member rest phase D is the limit of the penetration of thepenetrating member into the skin. Pain is reduced by minimizing theduration of the penetrating member introduction phase A-C so that thereis a fast incision to a certain penetration depth regardless of theduration of the deformation phase A and inflection point cutting B whichwill vary from user to user. Success rate is increased by measuring theexact depth of penetration from inflection point B to the limit ofpenetration in the penetrating member rest phase D. This measurementallows the penetrating member to always, or at least reliably, hit thecapillary beds which are a known distance underneath the surface of theskin.

The penetrating member retraction phase further comprises a primaryretraction phase E when the skin pushes the penetrating member out ofthe wound tract, a secondary retraction phase F when the penetratingmember starts to become dislodged and pulls in the opposite direction ofthe skin, and penetrating member exit phase G when the penetratingmember becomes free of the skin. Primary retraction is the result ofexerting a decreasing force to pull the penetrating member out of theskin as the penetrating member pulls away from the finger. Secondaryretraction is the result of exerting a force in the opposite directionto dislodge the penetrating member. Control is necessary to keep thewound tract open as blood flows up the wound tract. Blood volume isincreased by using a uniform velocity to retract the penetrating memberduring the penetrating member retraction phase E-G regardless of theforce required for the primary retraction phase E or secondaryretraction phase F, either of which may vary from user to user dependingon the properties of the user's skin.

Displacement versus time profile of a penetrating member for acontrolled penetrating member retraction can be plotted. Velocity vs.time profile of the penetrating member for the controlled retraction canalso be plotted. The penetrating member driver controls penetratingmember displacement and velocity at several steps in the lancing cycle,including when the penetrating member cuts the blood vessels to allowblood to pool 2130, and as the penetrating member retracts, regulatingthe retraction rate to allow the blood to flood the wound tract whilekeeping the wound flap from sealing the channel 2132 to permit blood toexit the wound.

The tenting process and retrograde motion of the penetrating memberduring the lancing cycle can be illustrated graphically which shows botha velocity versus time graph and a position versus time graph of apenetrating member tip during a lancing cycle that includes elastic andinelastic tenting. From point 0 to point A, the penetrating member isbeing accelerated from the initialization position or zero position.From point A to point B, the penetrating member is in ballistic orcoasting mode, with no additional power being delivered. At point B, thepenetrating member tip contacts the tissue and begins to tent the skinuntil it reaches a displacement C. As the penetrating member tipapproaches maximum displacement, braking force is applied to thepenetrating member until the penetrating member comes to a stop at pointD. The penetrating member then recoils in a retrograde direction duringthe settling phase of the lancing cycle indicated between D and E. Notethat the magnitude of inelastic tenting indicated in FIG. 48 isexaggerated for purposes of illustration.

The amount of inelastic tenting indicated by Z tends to be fairlyconsistent and small compared to the magnitude of the elastic tenting.Generally, the amount of inelastic tenting Z can be about 120 to about140 microns. As the magnitude of the inelastic tenting has a fairlyconstant value and is small compared to the magnitude of the elastictenting for most patients and skin types, the value for the total amountof tenting for the penetration stroke of the penetrating member iseffectively equal to the rearward displacement of the penetrating memberduring the settling phase as measured by the processor 193 plus apredetermined value for the inelastic recoil, such as 130 microns.Inelastic recoil for some embodiments can be about 100 to about 200microns. The ability to measure the magnitude of skin tenting for apatient is important to controlling the depth of penetration of thepenetrating member tip as the skin is generally known to vary inelasticity and other parameters due to age, time of day, level ofhydration, gender and pathological state.

This value for total tenting for the lancing cycle can then be used todetermine the various characteristics of the patient's skin. Once a bodyof tenting data is obtained for a given patient, this data can beanalyzed in order to predict the total penetrating member displacement,from the point of skin contact, necessary for a successful lancingprocedure. This enables the tissue penetration device to achieve a highsuccess rate and minimize pain for the user. A rolling average table canbe used to collect and store the tenting data for a patient with apointer to the last entry in the table. When a new entry is input, itcan replace the entry at the pointer and the pointer advances to thenext value. When an average is desired, all the values are added and thesum divided by the total number of entries by the processor 193. Similartechniques involving exponential decay (multiply by 0.95, add 0.05 timescurrent value, etc.) are also possible.

With regard to tenting of skin generally, some typical values relatingto penetration depth are now discussed. A cross sectional view of thelayers of the skin can be shown. In order to reliably obtain a useablesample of blood from the skin, it is desirable to have the penetratingmember tip reach the venuolar plexus of the skin. The stratum corneum istypically about 0.1 to about 0.6 mm thick and the distance from the topof the dermis to the venuole plexus can be from about 0.3 to about 1.4mm. Elastic tenting can have a magnitude of up to about 2 mm or so,specifically, about 0.2 to about 2.0 mm, with an average magnitude ofabout 1 mm. This means that the amount of penetrating memberdisplacement necessary to overcome the tenting can have a magnitudegreater than the thickness of skin necessary to penetrate in order toreach the venuolar plexus. The total penetrating member displacementfrom point of initial skin contact may have an average value of about1.7 to about 2.1 mm. In some embodiments, penetration depth and maximumpenetration depth may be about 0.5 mm to about 5 mm, specifically, about1 mm to about 3 mm. In some embodiments, a maximum penetration depth ofabout 0.5 to about 3 mm is useful.

In some embodiments, the penetrating member is withdrawn with less forceand a lower speed than the force and speed during the penetrationportion of the operation cycle. Withdrawal speed of the penetratingmember in some embodiments can be about 0.004 to about 0.5 m/s,specifically, about 0.006 to about 0.01 m/s. In other embodiments,useful withdrawal velocities can be about 0.001 to about 0.02 meters persecond, specifically, about 0.001 to about 0.01 meters per second. Forembodiments that use a relatively slow withdrawal velocity compared tothe penetration velocity, the withdrawal velocity may up to about 0.02meters per second. For such embodiments, a ratio of the averagepenetration velocity relative to the average withdrawal velocity can beabout 100 to about 1000. In embodiments where a relatively slowwithdrawal velocity is not important, a withdrawal velocity of about 2to about 10 meters per second may be used.

Another example of an embodiment of a velocity profile for a penetratingmember can be seen shown, which illustrates a penetrating member profilewith a fast entry velocity and a slow withdrawal velocity. A lancingprofile showing velocity of the penetrating member versus position. Thelancing profile starts at zero time and position and shows accelerationof the penetrating member towards the tissue from the electromagneticforce generated from the electromagnetic driver. At point A, the poweris shut off and the penetrating member begins to coast until it reachesthe skin indicated by B at which point, the velocity begins to decrease.At point C, the penetrating member has reached maximum displacement andsettles momentarily, typically for a time of about 8 milliseconds.

A retrograde withdrawal force is then imposed on the penetrating memberby the controllable driver, which is controlled by the processor tomaintain a withdrawal velocity of no more than about 0.006 to about 0.01meters/second. The same cycle is illustrated in the velocity versus timeplot of FIG. 151 where the penetrating member is accelerated from thestart point to point A. The penetrating member coasts from A to B wherethe penetrating member tip contacts tissue 233. The penetrating membertip then penetrates the tissue and slows with braking force eventuallyapplied as the maximum penetration depth is approached. The penetratingmember is stopped and settling between C and D. At D, the withdrawalphase begins and the penetrating member is slowly withdrawn until itreturns to the initialization point shown by E. Note that retrograderecoil from elastic and inelastic tenting was not shown in the lancingprofiles for purpose of illustration and clarity.

In another embodiment, the withdrawal phase may use a dual speedprofile, with the slow 0.006 to 0.01 meter per second speed used untilthe penetrating member is withdrawn past the contact point with thetissue, then a faster speed of 0.01 to 1 meters per second may be usedto shorten the complete cycle.

While the invention has been described and illustrated with reference tocertain particular embodiments thereof, those skilled in the art willappreciate that various adaptations, changes, modifications,substitutions, deletions, or additions of procedures and protocols maybe made without departing from the spirit and scope of the invention.For example, with any of the above embodiments, the location of thepenetrating member drive device may be varied, relative to thepenetrating members or the cartridge. With any of the above embodiments,the penetrating member tips may be uncovered during actuation (i.e.penetrating members do not pierce the penetrating member enclosure orprotective foil during launch). With any of the above embodiments, thepenetrating members may be a bare penetrating member during launch. Withany of the above embodiments, the penetrating members may be barepenetrating members prior to launch as this may allow for significantlytighter densities of penetrating members. In some embodiments, thepenetrating members may be bent, curved, textured, shaped, or otherwisetreated at a proximal end or area to facilitate handling by an actuator.The penetrating member may be configured to have a notch or groove tofacilitate coupling to a gripper. The notch or groove may be formedalong an elongate portion of the penetrating member. With any of theabove embodiments, the cavity may be on the bottom or the top of thecartridge, with the gripper on the other side. In some embodiments,analyte detecting members may be printed on the top, bottom, or side ofthe cavities. The front end of the cartridge maybe in contact with auser during lancing. The same driver may be used for advancing andretraction of the penetrating member. The penetrating member may have adiameters and length suitable for obtaining the blood volumes describedherein. The penetrating member driver may also be in substantially thesame plane as the cartridge. The driver may use a through hole or otheropening to engage a proximal end of a penetrating member to actuate thepenetrating member along a path into and out of the tissue.

Any of the features described in this application or any referencedisclosed herein may be adapted for use with any embodiment of thepresent invention. For example, the devices of the present invention mayalso be combined for use with injection penetrating members or needlesas described in commonly assigned, U.S. patent application Ser. No.10/127,395 filed Apr. 19, 2002 (now U.S. Pat. No. 7,025,774). An analytedetecting member to detect the presence of foil may also be included inthe lancing apparatus. For example, if a cavity has been used before,the foil or sterility barrier will be punched. The analyte detectingmember can detect if the cavity is fresh or not based on the status ofthe barrier. It should be understood that in optional embodiments, thesterility barrier may be designed to pierce a sterility barrier ofthickness that does not dull a tip of the penetrating member. Thelancing apparatus may also use improved drive mechanisms. For example, asolenoid force generator may be improved to try to increase the amountof force the solenoid can generate for a given current. A solenoid foruse with the present invention may have five coils and in the presentembodiment the slug is roughly the size of two coils. One change is toincrease the thickness of the outer metal shell or windings surround thecoils. By increasing the thickness, the flux will also be increased. Theslug may be split; two smaller slugs may also be used and offset by ½ ofa coil pitch. This allows more slugs to be approaching a coil where itcould be accelerated. This creates more events where a slug isapproaching a coil, creating a more efficient system.

In another optional alternative embodiment, a gripper in the inner endof the protective cavity may hold the penetrating member during shipmentand after use, eliminating the feature of using the foil, protectiveend, or other part to retain the used penetrating member. Some otheradvantages of the disclosed embodiments and features of additionalembodiments include: same mechanism for transferring the usedpenetrating members to a storage area; a high number of penetratingmembers such as 25, 50, 75, 100, 500, or more penetrating members may beput on a disk or cartridge; molded body about a lancet becomesunnecessary; manufacturing of multiple penetrating member devices issimplified through the use of cartridges; handling is possible of barerods metal wires, without any additional structural features, to actuatethem into tissue; maintaining extreme (better than 50 micron-lateral-and better than 20 micron vertical) precision in guiding; and storagesystem for new and used penetrating members, with individualcavities/slots is provided. The housing of the lancing device may alsobe sized to be ergonomically pleasing. In one embodiment, the device hasa width of about 56 mm, a length of about 105 mm and a thickness ofabout 15 mm. Additionally, some embodiments of the present invention maybe used with non-electrical force generators or drive mechanism. Forexample, the punch device and methods for releasing the penetratingmembers from sterile enclosures could be adapted for use with springbased launchers. The gripper using a frictional coupling may also beadapted for use with other drive technologies.

Still further optional features may be included with the presentinvention. For example, with any of the above embodiments, the locationof the penetrating member drive device may be varied, relative to thepenetrating members or the cartridge. With any of the above embodiments,the penetrating member tips may be uncovered during actuation (i.e.penetrating members do not pierce the penetrating member enclosure orprotective foil during launch). The penetrating members may be a barepenetrating member during launch. In some embodiments, the penetratingmember may be a patent needle. The same driver may be used for advancingand retraction of the penetrating member. Different analyte detectingmembers detecting different ranges of glucose concentration, differentanalytes, or the like may be combined for use with each penetratingmember. Non-potentiometric measurement techniques may also be used foranalyte detection. For example, direct electron transfer of glucoseoxidase molecules adsorbed onto carbon nanotube powder microelectrodemay be used to measure glucose levels. In some embodiments, the analytedetecting members may formed to flush with the cartridge so that a“well” is not formed. In some other embodiments, the analyte detectingmembers may formed to be substantially flush (within 200 microns or 100microns) with the cartridge surfaces. In all methods, nanoscopic wiregrowth can be carried out via chemical vapor deposition (CVD). In all ofthe embodiments of the invention, preferred nanoscopic wires may benanotubes. Any method useful for depositing a glucose oxidase or otheranalyte detection material on a nanowire or nanotube may be used withthe present invention. Additionally, for some embodiments, any of thecartridge shown above may be configured without any of the penetratingmembers, so that the cartridge is simply an analyte detecting device.Still further, the indexing of the cartridge may be such that adjacentcavities may not necessarily be used serially or sequentially. As anonlimiting example, every second cavity may be used sequentially, whichmeans that the cartridge will go through two rotations before every orsubstantially all of the cavities are used. As another nonlimitingexample, a cavity that is 3 cavities away, 4 cavities away, or Ncavities away may be the next one used. This may allow for greaterseparation between cavities containing penetrating members that werejust used and a fresh penetrating member to be used next. For any of theembodiments herein, they may be configured to provide the variousvelocity profiles described.

This application cross-references commonly assigned copending U.S.patent application Ser. No. 10/323,622 filed Dec. 18, 2002; commonlyassigned copending U.S. patent application Ser. No. 10/323,623 filedDec. 18, 2002; and commonly assigned copending U.S. patent applicationSer. No. 10/323,624 filed Dec. 18, 2002. This application is alsorelated to commonly assigned copending U.S. patent application Ser. Nos.10/335,142, 10/335,215, 10/335,258, 10/335,099, 10/335,219, 10/335,052,10/335,073, 10/335,220, 10/335,252, 10/335,218, 10/335,211, 10/335,257,10/335,217, 10/335,212, and 10/335,241, 10/335,183 filed Dec. 31, 2002.This application is also a continuation-in-part of commonly assigned,copending U.S. patent application Ser. No. 10/425,815 filed May 30,2003. This application is a continuation-in-part of commonly assigned,copending U.S. patent application Ser. No. 10/323,622 filed on Dec. 18,2002, which is a continuation-in-part of commonly assigned, U.S. patentapplication Ser. No. 10/127,395 filed Apr. 19, 2002 (now U.S. Pat. No.7,025,774). This application is also a continuation-in-part of commonlyassigned, copending U.S. patent application Ser. No. 10/237,261 filedSep. 5, 2002. This application is further a continuation-in-part ofcommonly assigned, copending U.S. patent application Ser. No. 10/420,535filed Apr. 21, 2003. This application is further a continuation-in-partof commonly assigned, copending U.S. patent application Ser. No.10/335,142 filed Dec. 31, 2002. This application is further acontinuation-in-part of commonly assigned, copending U.S. patentapplication Ser. No. 10/423,851 filed Apr. 24, 2003. This applicationalso claims the benefit of priority from commonly assigned, copendingU.S. Provisional Patent Application Ser. No. 60/422, filed Nov. 1, 2002;commonly assigned, copending U.S. Provisional Patent Application Ser.No. 60/424,429 filed Nov. 6, 2002; and commonly assigned, copending U.S.Provisional Patent Application Ser. No. 60/424,429 filed Nov. 20, 2002.All applications listed above are incorporated herein by reference forall purposes.

The publications discussed or cited herein are provided solely for theirdisclosure prior to the filing date of the present application. Nothingherein is to be construed as an admission that the present invention isnot entitled to antedate such publication by virtue of prior invention.Further, the dates of publication provided may be different from theactual publication dates which may need to be independently confirmed.All publications mentioned herein are incorporated herein by referenceto disclose and describe the structures and/or methods in connectionwith which the publications are cited. For ease of reference, U.S.Provisional Application Ser. Nos. 60/476,584, 60/478,040, 60/478,704,60/478,657, 60/478,682, and 60/507,689 are hereby fully incorporatedherein by reference for all purposes.

Expected variations or differences in the results are contemplated inaccordance with the objects and practices of the present invention. Itis intended, therefore, that the invention be defined by the scope ofthe claims which follow and that such claims be interpreted as broadlyas is reasonable.

1. A method of controlling penetrating member velocity, the methodcomprising: advancing the penetrating member to reach a first desiredvelocity; providing a controller for applying braking force; applyingvariable amounts of braking force and driving force to follow apredicted velocity profile, checking in each braking cycle whetherbraking force should be varied wherein a braking cycle is varied forpenetration depth control.
 2. The method of claim 1, further comprising:controlling penetrating member depth by using an electronic lancet drivesystem where penetration of the penetrating member in a directiontowards to the skin is determined by the amount of force applied by themotor to achieve a certain velocity at impact with the skin.
 3. A methodof body fluid sampling comprising: moving a penetrating member atvelocities conforming to a selectable velocity profile or motionwaveform; measuring force applied by user to a front end of a lancingdevice; determining amount of tissue tenting; recording tenting andforce; and applying a braking cycle in response to tenting.
 4. Themethod of claim 3 further comprising using force and tenting todetermine stratum corneum thickness based on a slope of multiple forceand tenting data points.
 5. A method of determining contact between atip of a penetrating member and target tissue of a patient comprising:(a) Providing a lancing device comprising a penetrating member driverhaving a position sensor and a processor that can determine the relativeposition and velocity of the penetrating member based on measuringrelative position of the penetrating member with respect to time; (b)Measuring a magnitude of deceleration of the penetrating member duringat least a portion of an inward cutting stroke of a lancing cycle andcomparing the magnitude of the measured deceleration to a known value ofdeceleration; and (c) Determining contact if the magnitude of themeasured deceleration is greater than the magnitude of the known valueof deceleration.